Table of Contents
Expressions can be used at several points in
SQL statements, such as in the
ORDER BY
or HAVING
clauses of
SELECT
statements, in the
WHERE
clause of a
SELECT
,
DELETE
, or
UPDATE
statement, or in
SET
statements. Expressions can be written using literal values, column
values, NULL
, built-in functions, stored
functions, user-defined functions, and operators. This chapter
describes the functions and operators that are permitted for writing
expressions in MySQL. Instructions for writing stored functions and
user-defined functions are given in
Section 23.2, “Using Stored Routines”, and
Section 28.4, “Adding Functions to MySQL”. See
Section 9.2.5, “Function Name Parsing and Resolution”, for the rules describing how
the server interprets references to different kinds of functions.
An expression that contains NULL
always produces
a NULL
value unless otherwise indicated in the
documentation for a particular function or operator.
By default, there must be no whitespace between a function name and the parenthesis following it. This helps the MySQL parser distinguish between function calls and references to tables or columns that happen to have the same name as a function. However, spaces around function arguments are permitted.
You can tell the MySQL server to accept spaces after function names
by starting it with the
--sql-mode=IGNORE_SPACE
option. (See
Section 5.1.10, “Server SQL Modes”.) Individual client programs can request
this behavior by using the CLIENT_IGNORE_SPACE
option for mysql_real_connect()
. In
either case, all function names become reserved words.
For the sake of brevity, most examples in this chapter display the output from the mysql program in abbreviated form. Rather than showing examples in this format:
mysql> SELECT MOD(29,9);
+-----------+
| mod(29,9) |
+-----------+
| 2 |
+-----------+
1 rows in set (0.00 sec)
This format is used instead:
mysql> SELECT MOD(29,9);
-> 2
Table 12.1 Functions and Operators
Name | Description |
---|---|
& |
Bitwise AND |
> |
Greater than operator |
>> |
Right shift |
>= |
Greater than or equal operator |
< |
Less than operator |
<> , != |
Not equal operator |
<< |
Left shift |
<= |
Less than or equal operator |
<=> |
NULL-safe equal to operator |
% , MOD |
Modulo operator |
* |
Multiplication operator |
+ |
Addition operator |
- |
Minus operator |
- |
Change the sign of the argument |
-> |
Return value from JSON column after evaluating path; equivalent to JSON_EXTRACT(). |
->> (introduced 5.7.13) |
Return value from JSON column after evaluating path and unquoting the result; equivalent to JSON_UNQUOTE(JSON_EXTRACT()). |
/ |
Division operator |
:= |
Assign a value |
= |
Assign a value (as part of a
SET
statement, or as part of the SET clause in an
UPDATE statement)
|
= |
Equal operator |
^ |
Bitwise XOR |
ABS() |
Return the absolute value |
ACOS() |
Return the arc cosine |
ADDDATE() |
Add time values (intervals) to a date value |
ADDTIME() |
Add time |
AES_DECRYPT() |
Decrypt using AES |
AES_ENCRYPT() |
Encrypt using AES |
AND , && |
Logical AND |
ANY_VALUE() |
Suppress ONLY_FULL_GROUP_BY value rejection |
Area() (deprecated) |
Return Polygon or MultiPolygon area |
AsBinary() , AsWKB() (deprecated) |
Convert from internal geometry format to WKB |
ASCII() |
Return numeric value of left-most character |
ASIN() |
Return the arc sine |
AsText() , AsWKT() (deprecated) |
Convert from internal geometry format to WKT |
ASYMMETRIC_DECRYPT() |
Decrypt ciphertext using private or public key |
ASYMMETRIC_DERIVE() |
Derive symmetric key from asymmetric keys |
ASYMMETRIC_ENCRYPT() |
Encrypt cleartext using private or public key |
ASYMMETRIC_SIGN() |
Generate signature from digest |
ASYMMETRIC_VERIFY() |
Verify that signature matches digest |
ATAN() |
Return the arc tangent |
ATAN2() , ATAN() |
Return the arc tangent of the two arguments |
AVG() |
Return the average value of the argument |
BENCHMARK() |
Repeatedly execute an expression |
BETWEEN ... AND ... |
Whether a value is within a range of values |
BIN() |
Return a string containing binary representation of a number |
BINARY |
Cast a string to a binary string |
BIT_AND() |
Return bitwise AND |
BIT_COUNT() |
Return the number of bits that are set |
BIT_LENGTH() |
Return length of argument in bits |
BIT_OR() |
Return bitwise OR |
BIT_XOR() |
Return bitwise XOR |
Buffer() (deprecated) |
Return geometry of points within given distance from geometry |
CASE |
Case operator |
CAST() |
Cast a value as a certain type |
CEIL() |
Return the smallest integer value not less than the argument |
CEILING() |
Return the smallest integer value not less than the argument |
Centroid() (deprecated) |
Return centroid as a point |
CHAR() |
Return the character for each integer passed |
CHAR_LENGTH() |
Return number of characters in argument |
CHARACTER_LENGTH() |
Synonym for CHAR_LENGTH() |
CHARSET() |
Return the character set of the argument |
COALESCE() |
Return the first non-NULL argument |
COERCIBILITY() |
Return the collation coercibility value of the string argument |
COLLATION() |
Return the collation of the string argument |
COMPRESS() |
Return result as a binary string |
CONCAT() |
Return concatenated string |
CONCAT_WS() |
Return concatenate with separator |
CONNECTION_ID() |
Return the connection ID (thread ID) for the connection |
Contains() (deprecated) |
Whether MBR of one geometry contains MBR of another |
CONV() |
Convert numbers between different number bases |
CONVERT() |
Cast a value as a certain type |
CONVERT_TZ() |
Convert from one time zone to another |
ConvexHull() (deprecated) |
Return convex hull of geometry |
COS() |
Return the cosine |
COT() |
Return the cotangent |
COUNT() |
Return a count of the number of rows returned |
COUNT(DISTINCT) |
Return the count of a number of different values |
CRC32() |
Compute a cyclic redundancy check value |
CREATE_ASYMMETRIC_PRIV_KEY() |
Create private key |
CREATE_ASYMMETRIC_PUB_KEY() |
Create public key |
CREATE_DH_PARAMETERS() |
Generate shared DH secret |
CREATE_DIGEST() |
Generate digest from string |
Crosses() (deprecated) |
Whether one geometry crosses another |
CURDATE() |
Return the current date |
CURRENT_DATE() , CURRENT_DATE |
Synonyms for CURDATE() |
CURRENT_TIME() , CURRENT_TIME |
Synonyms for CURTIME() |
CURRENT_TIMESTAMP() , CURRENT_TIMESTAMP |
Synonyms for NOW() |
CURRENT_USER() , CURRENT_USER |
The authenticated user name and host name |
CURTIME() |
Return the current time |
DATABASE() |
Return the default (current) database name |
DATE() |
Extract the date part of a date or datetime expression |
DATE_ADD() |
Add time values (intervals) to a date value |
DATE_FORMAT() |
Format date as specified |
DATE_SUB() |
Subtract a time value (interval) from a date |
DATEDIFF() |
Subtract two dates |
DAY() |
Synonym for DAYOFMONTH() |
DAYNAME() |
Return the name of the weekday |
DAYOFMONTH() |
Return the day of the month (0-31) |
DAYOFWEEK() |
Return the weekday index of the argument |
DAYOFYEAR() |
Return the day of the year (1-366) |
DECODE() (deprecated) |
Decode a string encrypted using ENCODE() |
DEFAULT() |
Return the default value for a table column |
DEGREES() |
Convert radians to degrees |
DES_DECRYPT() (deprecated) |
Decrypt a string |
DES_ENCRYPT() (deprecated) |
Encrypt a string |
Dimension() (deprecated) |
Dimension of geometry |
Disjoint() (deprecated) |
Whether MBRs of two geometries are disjoint |
Distance() (deprecated) |
The distance of one geometry from another |
DIV |
Integer division |
ELT() |
Return string at index number |
ENCODE() (deprecated) |
Encode a string |
ENCRYPT() (deprecated) |
Encrypt a string |
EndPoint() (deprecated) |
End Point of LineString |
Envelope() (deprecated) |
Return MBR of geometry |
Equals() (deprecated) |
Whether MBRs of two geometries are equal |
EXP() |
Raise to the power of |
EXPORT_SET() |
Return a string such that for every bit set in the value bits, you get an on string and for every unset bit, you get an off string |
ExteriorRing() (deprecated) |
Return exterior ring of Polygon |
EXTRACT() |
Extract part of a date |
ExtractValue() |
Extract a value from an XML string using XPath notation |
FIELD() |
Index (position) of first argument in subsequent arguments |
FIND_IN_SET() |
Index (position) of first argument within second argument |
FLOOR() |
Return the largest integer value not greater than the argument |
FORMAT() |
Return a number formatted to specified number of decimal places |
FOUND_ROWS() |
For a SELECT with a LIMIT clause, the number of rows that would be returned were there no LIMIT clause |
FROM_BASE64() |
Decode base64 encoded string and return result |
FROM_DAYS() |
Convert a day number to a date |
FROM_UNIXTIME() |
Format Unix timestamp as a date |
GeomCollFromText() , GeometryCollectionFromText() (deprecated) |
Return geometry collection from WKT |
GeomCollFromWKB() , GeometryCollectionFromWKB() (deprecated) |
Return geometry collection from WKB |
GeometryCollection() |
Construct geometry collection from geometries |
GeometryN() (deprecated) |
Return N-th geometry from geometry collection |
GeometryType() (deprecated) |
Return name of geometry type |
GeomFromText() , GeometryFromText() (deprecated) |
Return geometry from WKT |
GeomFromWKB() , GeometryFromWKB() (deprecated) |
Return geometry from WKB |
GET_FORMAT() |
Return a date format string |
GET_LOCK() |
Get a named lock |
GLength() (deprecated) |
Return length of LineString |
GREATEST() |
Return the largest argument |
GROUP_CONCAT() |
Return a concatenated string |
GTID_SUBSET() |
Return true if all GTIDs in subset are also in set; otherwise false. |
GTID_SUBTRACT() |
Return all GTIDs in set that are not in subset. |
HEX() |
Hexadecimal representation of decimal or string value |
HOUR() |
Extract the hour |
IF() |
If/else construct |
IFNULL() |
Null if/else construct |
IN() |
Whether a value is within a set of values |
INET_ATON() |
Return the numeric value of an IP address |
INET_NTOA() |
Return the IP address from a numeric value |
INET6_ATON() |
Return the numeric value of an IPv6 address |
INET6_NTOA() |
Return the IPv6 address from a numeric value |
INSERT() |
Insert substring at specified position up to specified number of characters |
INSTR() |
Return the index of the first occurrence of substring |
InteriorRingN() (deprecated) |
Return N-th interior ring of Polygon |
Intersects() (deprecated) |
Whether MBRs of two geometries intersect |
INTERVAL() |
Return the index of the argument that is less than the first argument |
IS |
Test a value against a boolean |
IS_FREE_LOCK() |
Whether the named lock is free |
IS_IPV4() |
Whether argument is an IPv4 address |
IS_IPV4_COMPAT() |
Whether argument is an IPv4-compatible address |
IS_IPV4_MAPPED() |
Whether argument is an IPv4-mapped address |
IS_IPV6() |
Whether argument is an IPv6 address |
IS NOT |
Test a value against a boolean |
IS NOT NULL |
NOT NULL value test |
IS NULL |
NULL value test |
IS_USED_LOCK() |
Whether the named lock is in use; return connection identifier if true |
IsClosed() (deprecated) |
Whether a geometry is closed and simple |
IsEmpty() (deprecated) |
Placeholder function |
ISNULL() |
Test whether the argument is NULL |
IsSimple() (deprecated) |
Whether a geometry is simple |
JSON_APPEND() (deprecated) |
Append data to JSON document |
JSON_ARRAY() |
Create JSON array |
JSON_ARRAY_APPEND() |
Append data to JSON document |
JSON_ARRAY_INSERT() |
Insert into JSON array |
JSON_ARRAYAGG() (introduced 5.7.22) |
Return result set as a single JSON array |
JSON_CONTAINS() |
Whether JSON document contains specific object at path |
JSON_CONTAINS_PATH() |
Whether JSON document contains any data at path |
JSON_DEPTH() |
Maximum depth of JSON document |
JSON_EXTRACT() |
Return data from JSON document |
JSON_INSERT() |
Insert data into JSON document |
JSON_KEYS() |
Array of keys from JSON document |
JSON_LENGTH() |
Number of elements in JSON document |
JSON_MERGE() (deprecated 5.7.22) |
Merge JSON documents, preserving duplicate keys. Deprecated synonym for JSON_MERGE_PRESERVE() |
JSON_MERGE_PATCH() (introduced 5.7.22) |
Merge JSON documents, replacing values of duplicate keys |
JSON_MERGE_PRESERVE() (introduced 5.7.22) |
Merge JSON documents, preserving duplicate keys |
JSON_OBJECT() |
Create JSON object |
JSON_OBJECTAGG() (introduced 5.7.22) |
Return result set as a single JSON object |
JSON_PRETTY() (introduced 5.7.22) |
Print a JSON document in human-readable format |
JSON_QUOTE() |
Quote JSON document |
JSON_REMOVE() |
Remove data from JSON document |
JSON_REPLACE() |
Replace values in JSON document |
JSON_SEARCH() |
Path to value within JSON document |
JSON_SET() |
Insert data into JSON document |
JSON_STORAGE_SIZE() (introduced 5.7.22) |
Space used for storage of binary representation of a JSON document |
JSON_TYPE() |
Type of JSON value |
JSON_UNQUOTE() |
Unquote JSON value |
JSON_VALID() |
Whether JSON value is valid |
LAST_DAY |
Return the last day of the month for the argument |
LAST_INSERT_ID() |
Value of the AUTOINCREMENT column for the last INSERT |
LCASE() |
Synonym for LOWER() |
LEAST() |
Return the smallest argument |
LEFT() |
Return the leftmost number of characters as specified |
LENGTH() |
Return the length of a string in bytes |
LIKE |
Simple pattern matching |
LineFromText() , LineStringFromText() (deprecated) |
Construct LineString from WKT |
LineFromWKB() , LineStringFromWKB() (deprecated) |
Construct LineString from WKB |
LineString() |
Construct LineString from Point values |
LN() |
Return the natural logarithm of the argument |
LOAD_FILE() |
Load the named file |
LOCALTIME() , LOCALTIME |
Synonym for NOW() |
LOCALTIMESTAMP , LOCALTIMESTAMP() |
Synonym for NOW() |
LOCATE() |
Return the position of the first occurrence of substring |
LOG() |
Return the natural logarithm of the first argument |
LOG10() |
Return the base-10 logarithm of the argument |
LOG2() |
Return the base-2 logarithm of the argument |
LOWER() |
Return the argument in lowercase |
LPAD() |
Return the string argument, left-padded with the specified string |
LTRIM() |
Remove leading spaces |
MAKE_SET() |
Return a set of comma-separated strings that have the corresponding bit in bits set |
MAKEDATE() |
Create a date from the year and day of year |
MAKETIME() |
Create time from hour, minute, second |
MASTER_POS_WAIT() |
Block until the slave has read and applied all updates up to the specified position |
MATCH |
Perform full-text search |
MAX() |
Return the maximum value |
MBRContains() |
Whether MBR of one geometry contains MBR of another |
MBRCoveredBy() |
Whether one MBR is covered by another |
MBRCovers() |
Whether one MBR covers another |
MBRDisjoint() |
Whether MBRs of two geometries are disjoint |
MBREqual() (deprecated) |
Whether MBRs of two geometries are equal |
MBREquals() |
Whether MBRs of two geometries are equal |
MBRIntersects() |
Whether MBRs of two geometries intersect |
MBROverlaps() |
Whether MBRs of two geometries overlap |
MBRTouches() |
Whether MBRs of two geometries touch |
MBRWithin() |
Whether MBR of one geometry is within MBR of another |
MD5() |
Calculate MD5 checksum |
MICROSECOND() |
Return the microseconds from argument |
MID() |
Return a substring starting from the specified position |
MIN() |
Return the minimum value |
MINUTE() |
Return the minute from the argument |
MLineFromText() , MultiLineStringFromText() (deprecated) |
Construct MultiLineString from WKT |
MLineFromWKB() , MultiLineStringFromWKB() (deprecated) |
Construct MultiLineString from WKB |
MOD() |
Return the remainder |
MONTH() |
Return the month from the date passed |
MONTHNAME() |
Return the name of the month |
MPointFromText() , MultiPointFromText() (deprecated) |
Construct MultiPoint from WKT |
MPointFromWKB() , MultiPointFromWKB() (deprecated) |
Construct MultiPoint from WKB |
MPolyFromText() , MultiPolygonFromText() (deprecated) |
Construct MultiPolygon from WKT |
MPolyFromWKB() , MultiPolygonFromWKB() (deprecated) |
Construct MultiPolygon from WKB |
MultiLineString() |
Contruct MultiLineString from LineString values |
MultiPoint() |
Construct MultiPoint from Point values |
MultiPolygon() |
Construct MultiPolygon from Polygon values |
NAME_CONST() |
Cause the column to have the given name |
NOT , ! |
Negates value |
NOT BETWEEN ... AND ... |
Whether a value is not within a range of values |
NOT IN() |
Whether a value is not within a set of values |
NOT LIKE |
Negation of simple pattern matching |
NOT REGEXP |
Negation of REGEXP |
NOW() |
Return the current date and time |
NULLIF() |
Return NULL if expr1 = expr2 |
NumGeometries() (deprecated) |
Return number of geometries in geometry collection |
NumInteriorRings() (deprecated) |
Return number of interior rings in Polygon |
NumPoints() (deprecated) |
Return number of points in LineString |
OCT() |
Return a string containing octal representation of a number |
OCTET_LENGTH() |
Synonym for LENGTH() |
OR , || |
Logical OR |
ORD() |
Return character code for leftmost character of the argument |
Overlaps() (deprecated) |
Whether MBRs of two geometries overlap |
PASSWORD() (deprecated) |
Calculate and return a password string |
PERIOD_ADD() |
Add a period to a year-month |
PERIOD_DIFF() |
Return the number of months between periods |
PI() |
Return the value of pi |
Point() |
Construct Point from coordinates |
PointFromText() (deprecated) |
Construct Point from WKT |
PointFromWKB() (deprecated) |
Construct Point from WKB |
PointN() (deprecated) |
Return N-th point from LineString |
PolyFromText() , PolygonFromText() (deprecated) |
Construct Polygon from WKT |
PolyFromWKB() , PolygonFromWKB() (deprecated) |
Construct Polygon from WKB |
Polygon() |
Construct Polygon from LineString arguments |
POSITION() |
Synonym for LOCATE() |
POW() |
Return the argument raised to the specified power |
POWER() |
Return the argument raised to the specified power |
PROCEDURE ANALYSE() (deprecated 5.7.18) |
Analyze the results of a query |
QUARTER() |
Return the quarter from a date argument |
QUOTE() |
Escape the argument for use in an SQL statement |
RADIANS() |
Return argument converted to radians |
RAND() |
Return a random floating-point value |
RANDOM_BYTES() |
Return a random byte vector |
REGEXP |
Whether string matches regular expression |
RELEASE_ALL_LOCKS() |
Release all current named locks |
RELEASE_LOCK() |
Release the named lock |
REPEAT() |
Repeat a string the specified number of times |
REPLACE() |
Replace occurrences of a specified string |
REVERSE() |
Reverse the characters in a string |
RIGHT() |
Return the specified rightmost number of characters |
RLIKE |
Whether string matches regular expression |
ROUND() |
Round the argument |
ROW_COUNT() |
The number of rows updated |
RPAD() |
Append string the specified number of times |
RTRIM() |
Remove trailing spaces |
SCHEMA() |
Synonym for DATABASE() |
SEC_TO_TIME() |
Converts seconds to 'hh:mm:ss' format |
SECOND() |
Return the second (0-59) |
SESSION_USER() |
Synonym for USER() |
SHA1() , SHA() |
Calculate an SHA-1 160-bit checksum |
SHA2() |
Calculate an SHA-2 checksum |
SIGN() |
Return the sign of the argument |
SIN() |
Return the sine of the argument |
SLEEP() |
Sleep for a number of seconds |
SOUNDEX() |
Return a soundex string |
SOUNDS LIKE |
Compare sounds |
SPACE() |
Return a string of the specified number of spaces |
SQRT() |
Return the square root of the argument |
SRID() (deprecated) |
Return spatial reference system ID for geometry |
ST_Area() |
Return Polygon or MultiPolygon area |
ST_AsBinary() , ST_AsWKB() |
Convert from internal geometry format to WKB |
ST_AsGeoJSON() |
Generate GeoJSON object from geometry |
ST_AsText() , ST_AsWKT() |
Convert from internal geometry format to WKT |
ST_Buffer() |
Return geometry of points within given distance from geometry |
ST_Buffer_Strategy() |
Produce strategy option for ST_Buffer() |
ST_Centroid() |
Return centroid as a point |
ST_Contains() |
Whether one geometry contains another |
ST_ConvexHull() |
Return convex hull of geometry |
ST_Crosses() |
Whether one geometry crosses another |
ST_Difference() |
Return point set difference of two geometries |
ST_Dimension() |
Dimension of geometry |
ST_Disjoint() |
Whether one geometry is disjoint from another |
ST_Distance() |
The distance of one geometry from another |
ST_Distance_Sphere() |
Minimum distance on earth between two geometries |
ST_EndPoint() |
End Point of LineString |
ST_Envelope() |
Return MBR of geometry |
ST_Equals() |
Whether one geometry is equal to another |
ST_ExteriorRing() |
Return exterior ring of Polygon |
ST_GeoHash() |
Produce a geohash value |
ST_GeomCollFromText() , ST_GeometryCollectionFromText() , ST_GeomCollFromTxt() |
Return geometry collection from WKT |
ST_GeomCollFromWKB() , ST_GeometryCollectionFromWKB() |
Return geometry collection from WKB |
ST_GeometryN() |
Return N-th geometry from geometry collection |
ST_GeometryType() |
Return name of geometry type |
ST_GeomFromGeoJSON() |
Generate geometry from GeoJSON object |
ST_GeomFromText() , ST_GeometryFromText() |
Return geometry from WKT |
ST_GeomFromWKB() , ST_GeometryFromWKB() |
Return geometry from WKB |
ST_InteriorRingN() |
Return N-th interior ring of Polygon |
ST_Intersection() |
Return point set intersection of two geometries |
ST_Intersects() |
Whether one geometry intersects another |
ST_IsClosed() |
Whether a geometry is closed and simple |
ST_IsEmpty() |
Placeholder function |
ST_IsSimple() |
Whether a geometry is simple |
ST_IsValid() |
Whether a geometry is valid |
ST_LatFromGeoHash() |
Return latitude from geohash value |
ST_Length() |
Return length of LineString |
ST_LineFromText() , ST_LineStringFromText() |
Construct LineString from WKT |
ST_LineFromWKB() , ST_LineStringFromWKB() |
Construct LineString from WKB |
ST_LongFromGeoHash() |
Return longitude from geohash value |
ST_MakeEnvelope() |
Rectangle around two points |
ST_MLineFromText() , ST_MultiLineStringFromText() |
Construct MultiLineString from WKT |
ST_MLineFromWKB() , ST_MultiLineStringFromWKB() |
Construct MultiLineString from WKB |
ST_MPointFromText() , ST_MultiPointFromText() |
Construct MultiPoint from WKT |
ST_MPointFromWKB() , ST_MultiPointFromWKB() |
Construct MultiPoint from WKB |
ST_MPolyFromText() , ST_MultiPolygonFromText() |
Construct MultiPolygon from WKT |
ST_MPolyFromWKB() , ST_MultiPolygonFromWKB() |
Construct MultiPolygon from WKB |
ST_NumGeometries() |
Return number of geometries in geometry collection |
ST_NumInteriorRing() , ST_NumInteriorRings() |
Return number of interior rings in Polygon |
ST_NumPoints() |
Return number of points in LineString |
ST_Overlaps() |
Whether one geometry overlaps another |
ST_PointFromGeoHash() |
Convert geohash value to POINT value |
ST_PointFromText() |
Construct Point from WKT |
ST_PointFromWKB() |
Construct Point from WKB |
ST_PointN() |
Return N-th point from LineString |
ST_PolyFromText() , ST_PolygonFromText() |
Construct Polygon from WKT |
ST_PolyFromWKB() , ST_PolygonFromWKB() |
Construct Polygon from WKB |
ST_Simplify() |
Return simplified geometry |
ST_SRID() |
Return spatial reference system ID for geometry |
ST_StartPoint() |
Start Point of LineString |
ST_SymDifference() |
Return point set symmetric difference of two geometries |
ST_Touches() |
Whether one geometry touches another |
ST_Union() |
Return point set union of two geometries |
ST_Validate() |
Return validated geometry |
ST_Within() |
Whether one geometry is within another |
ST_X() |
Return X coordinate of Point |
ST_Y() |
Return Y coordinate of Point |
StartPoint() (deprecated) |
Start Point of LineString |
STD() |
Return the population standard deviation |
STDDEV() |
Return the population standard deviation |
STDDEV_POP() |
Return the population standard deviation |
STDDEV_SAMP() |
Return the sample standard deviation |
STR_TO_DATE() |
Convert a string to a date |
STRCMP() |
Compare two strings |
SUBDATE() |
Synonym for DATE_SUB() when invoked with three arguments |
SUBSTR() |
Return the substring as specified |
SUBSTRING() |
Return the substring as specified |
SUBSTRING_INDEX() |
Return a substring from a string before the specified number of occurrences of the delimiter |
SUBTIME() |
Subtract times |
SUM() |
Return the sum |
SYSDATE() |
Return the time at which the function executes |
SYSTEM_USER() |
Synonym for USER() |
TAN() |
Return the tangent of the argument |
TIME() |
Extract the time portion of the expression passed |
TIME_FORMAT() |
Format as time |
TIME_TO_SEC() |
Return the argument converted to seconds |
TIMEDIFF() |
Subtract time |
TIMESTAMP() |
With a single argument, this function returns the date or datetime expression; with two arguments, the sum of the arguments |
TIMESTAMPADD() |
Add an interval to a datetime expression |
TIMESTAMPDIFF() |
Subtract an interval from a datetime expression |
TO_BASE64() |
Return the argument converted to a base-64 string |
TO_DAYS() |
Return the date argument converted to days |
TO_SECONDS() |
Return the date or datetime argument converted to seconds since Year 0 |
Touches() (deprecated) |
Whether one geometry touches another |
TRIM() |
Remove leading and trailing spaces |
TRUNCATE() |
Truncate to specified number of decimal places |
UCASE() |
Synonym for UPPER() |
UNCOMPRESS() |
Uncompress a string compressed |
UNCOMPRESSED_LENGTH() |
Return the length of a string before compression |
UNHEX() |
Return a string containing hex representation of a number |
UNIX_TIMESTAMP() |
Return a Unix timestamp |
UpdateXML() |
Return replaced XML fragment |
UPPER() |
Convert to uppercase |
USER() |
The user name and host name provided by the client |
UTC_DATE() |
Return the current UTC date |
UTC_TIME() |
Return the current UTC time |
UTC_TIMESTAMP() |
Return the current UTC date and time |
UUID() |
Return a Universal Unique Identifier (UUID) |
UUID_SHORT() |
Return an integer-valued universal identifier |
VALIDATE_PASSWORD_STRENGTH() |
Determine strength of password |
VALUES() |
Define the values to be used during an INSERT |
VAR_POP() |
Return the population standard variance |
VAR_SAMP() |
Return the sample variance |
VARIANCE() |
Return the population standard variance |
VERSION() |
Return a string that indicates the MySQL server version |
WAIT_FOR_EXECUTED_GTID_SET() |
Wait until the given GTIDs have executed on the slave. |
WAIT_UNTIL_SQL_THREAD_AFTER_GTIDS() |
Use WAIT_FOR_EXECUTED_GTID_SET() .
|
WEEK() |
Return the week number |
WEEKDAY() |
Return the weekday index |
WEEKOFYEAR() |
Return the calendar week of the date (1-53) |
WEIGHT_STRING() |
Return the weight string for a string |
Within() (deprecated) |
Whether MBR of one geometry is within MBR of another |
X() (deprecated) |
Return X coordinate of Point |
XOR |
Logical XOR |
Y() (deprecated) |
Return Y coordinate of Point |
YEAR() |
Return the year |
YEARWEEK() |
Return the year and week |
| |
Bitwise OR |
~ |
Bitwise inversion |
When an operator is used with operands of different types, type conversion occurs to make the operands compatible. Some conversions occur implicitly. For example, MySQL automatically converts strings to numbers as necessary, and vice versa.
mysql>SELECT 1+'1';
-> 2 mysql>SELECT CONCAT(2,' test');
-> '2 test'
It is also possible to convert a number to a string explicitly
using the CAST()
function.
Conversion occurs implicitly with the
CONCAT()
function because it
expects string arguments.
mysql>SELECT 38.8, CAST(38.8 AS CHAR);
-> 38.8, '38.8' mysql>SELECT 38.8, CONCAT(38.8);
-> 38.8, '38.8'
See later in this section for information about the character set
of implicit number-to-string conversions, and for modified rules
that apply to CREATE TABLE ... SELECT
statements.
The following rules describe how conversion occurs for comparison operations:
If one or both arguments are NULL
, the
result of the comparison is NULL
, except
for the NULL
-safe
<=>
equality comparison operator. For NULL <=>
NULL
, the result is true. No conversion is needed.
If both arguments in a comparison operation are strings, they are compared as strings.
If both arguments are integers, they are compared as integers.
Hexadecimal values are treated as binary strings if not compared to a number.
If one of the arguments is a
TIMESTAMP
or
DATETIME
column and the other
argument is a constant, the constant is converted to a
timestamp before the comparison is performed. This is done to
be more ODBC-friendly. This is not done for the arguments to
IN()
. To be safe, always use
complete datetime, date, or time strings when doing
comparisons. For example, to achieve best results when using
BETWEEN
with date or time values,
use CAST()
to explicitly
convert the values to the desired data type.
A single-row subquery from a table or tables is not considered
a constant. For example, if a subquery returns an integer to
be compared to a DATETIME
value, the comparison is done as two integers. The integer is
not converted to a temporal value. To compare the operands as
DATETIME
values, use
CAST()
to explicitly convert
the subquery value to DATETIME
.
If one of the arguments is a decimal value, comparison depends on the other argument. The arguments are compared as decimal values if the other argument is a decimal or integer value, or as floating-point values if the other argument is a floating-point value.
In all other cases, the arguments are compared as floating-point (real) numbers. For example, a comparison of string and numeric operands takes places as a comparison of floating-point numbers.
For information about conversion of values from one temporal type to another, see Section 11.2.8, “Conversion Between Date and Time Types”.
Comparison of JSON values takes place at two levels. The first level of comparison is based on the JSON types of the compared values. If the types differ, the comparison result is determined solely by which type has higher precedence. If the two values have the same JSON type, a second level of comparison occurs using type-specific rules. For comparison of JSON and non-JSON values, the non-JSON value is converted to JSON and the values compared as JSON values. For details, see Comparison and Ordering of JSON Values.
The following examples illustrate conversion of strings to numbers for comparison operations:
mysql>SELECT 1 > '6x';
-> 0 mysql>SELECT 7 > '6x';
-> 1 mysql>SELECT 0 > 'x6';
-> 0 mysql>SELECT 0 = 'x6';
-> 1
For comparisons of a string column with a number, MySQL cannot use
an index on the column to look up the value quickly. If
str_col
is an indexed string column,
the index cannot be used when performing the lookup in the
following statement:
SELECT * FROMtbl_name
WHEREstr_col
=1;
The reason for this is that there are many different strings that
may convert to the value 1
, such as
'1'
, ' 1'
, or
'1a'
.
Comparisons that use floating-point numbers (or values that are converted to floating-point numbers) are approximate because such numbers are inexact. This might lead to results that appear inconsistent:
mysql>SELECT '18015376320243458' = 18015376320243458;
-> 1 mysql>SELECT '18015376320243459' = 18015376320243459;
-> 0
Such results can occur because the values are converted to floating-point numbers, which have only 53 bits of precision and are subject to rounding:
mysql> SELECT '18015376320243459'+0.0;
-> 1.8015376320243e+16
Furthermore, the conversion from string to floating-point and from integer to floating-point do not necessarily occur the same way. The integer may be converted to floating-point by the CPU, whereas the string is converted digit by digit in an operation that involves floating-point multiplications.
The results shown will vary on different systems, and can be
affected by factors such as computer architecture or the compiler
version or optimization level. One way to avoid such problems is
to use CAST()
so that a value is
not converted implicitly to a float-point number:
mysql> SELECT CAST('18015376320243459' AS UNSIGNED) = 18015376320243459;
-> 1
For more information about floating-point comparisons, see Section B.4.4.8, “Problems with Floating-Point Values”.
The server includes dtoa
, a conversion library
that provides the basis for improved conversion between string or
DECIMAL
values and
approximate-value
(FLOAT
/DOUBLE
)
numbers:
Consistent conversion results across platforms, which eliminates, for example, Unix versus Windows conversion differences.
Accurate representation of values in cases where results previously did not provide sufficient precision, such as for values close to IEEE limits.
Conversion of numbers to string format with the best possible
precision. The precision of dtoa
is always
the same or better than that of the standard C library
functions.
Because the conversions produced by this library differ in some
cases from non-dtoa
results, the potential
exists for incompatibilities in applications that rely on previous
results. For example, applications that depend on a specific exact
result from previous conversions might need adjustment to
accommodate additional precision.
The dtoa
library provides conversions with the
following properties. D
represents a
value with a DECIMAL
or string
representation, and F
represents a
floating-point number in native binary (IEEE) format.
F
->
D
conversion is done with the best
possible precision, returning D
as
the shortest string that yields F
when read back in and rounded to the nearest value in native
binary format as specified by IEEE.
D
->
F
conversion is done such that
F
is the nearest native binary
number to the input decimal string
D
.
These properties imply that F
->
D
-> F
conversions are lossless unless F
is
-inf
, +inf
, or
NaN
. The latter values are not supported
because the SQL standard defines them as invalid values for
FLOAT
or
DOUBLE
.
For D
->
F
-> D
conversions, a sufficient condition for losslessness is that
D
uses 15 or fewer digits of precision,
is not a denormal value, -inf
,
+inf
, or NaN
. In some cases,
the conversion is lossless even if D
has more than 15 digits of precision, but this is not always the
case.
Implicit conversion of a numeric or temporal value to string
produces a value that has a character set and collation determined
by the character_set_connection
and collation_connection
system
variables. (These variables commonly are set with
SET NAMES
. For information about
connection character sets, see
Section 10.4, “Connection Character Sets and Collations”.)
This means that such a conversion results in a character
(nonbinary) string (a CHAR
,
VARCHAR
, or
LONGTEXT
value), except in the case
that the connection character set is set to
binary
. In that case, the conversion result is
a binary string (a BINARY
,
VARBINARY
, or
LONGBLOB
value).
For integer expressions, the preceding remarks about expression evaluation apply somewhat differently for expression assignment; for example, in a statement such as this:
CREATE TABLE t SELECT integer_expr
;
In this case, the table in the column resulting from the
expression has type INT
or
BIGINT
depending on the length of
the integer expression. If the maximum length of the expression
does not fit in an INT
,
BIGINT
is used instead. The length
is taken from the max_length
value of the
SELECT
result set metadata (see
Section 27.7.4, “C API Data Structures”). This means that you can
force a BIGINT
rather than
INT
by use of a sufficiently long
expression:
CREATE TABLE t SELECT 000000000000000000000;
Table 12.2 Operators
Name | Description |
---|---|
& |
Bitwise AND |
> |
Greater than operator |
>> |
Right shift |
>= |
Greater than or equal operator |
< |
Less than operator |
<> , != |
Not equal operator |
<< |
Left shift |
<= |
Less than or equal operator |
<=> |
NULL-safe equal to operator |
% , MOD |
Modulo operator |
* |
Multiplication operator |
+ |
Addition operator |
- |
Minus operator |
- |
Change the sign of the argument |
-> |
Return value from JSON column after evaluating path; equivalent to JSON_EXTRACT(). |
->> (introduced 5.7.13) |
Return value from JSON column after evaluating path and unquoting the result; equivalent to JSON_UNQUOTE(JSON_EXTRACT()). |
/ |
Division operator |
:= |
Assign a value |
= |
Assign a value (as part of a
SET
statement, or as part of the SET clause in an
UPDATE statement)
|
= |
Equal operator |
^ |
Bitwise XOR |
AND , && |
Logical AND |
BETWEEN ... AND ... |
Whether a value is within a range of values |
BINARY |
Cast a string to a binary string |
CASE |
Case operator |
DIV |
Integer division |
IN() |
Whether a value is within a set of values |
IS |
Test a value against a boolean |
IS NOT |
Test a value against a boolean |
IS NOT NULL |
NOT NULL value test |
IS NULL |
NULL value test |
LIKE |
Simple pattern matching |
NOT , ! |
Negates value |
NOT BETWEEN ... AND ... |
Whether a value is not within a range of values |
NOT IN() |
Whether a value is not within a set of values |
NOT LIKE |
Negation of simple pattern matching |
NOT REGEXP |
Negation of REGEXP |
OR , || |
Logical OR |
REGEXP |
Whether string matches regular expression |
RLIKE |
Whether string matches regular expression |
SOUNDS LIKE |
Compare sounds |
XOR |
Logical XOR |
| |
Bitwise OR |
~ |
Bitwise inversion |
Operator precedences are shown in the following list, from highest precedence to the lowest. Operators that are shown together on a line have the same precedence.
INTERVAL BINARY, COLLATE ! - (unary minus), ~ (unary bit inversion) ^ *, /, DIV, %, MOD -, + <<, >> & | = (comparison), <=>, >=, >, <=, <, <>, !=, IS, LIKE, REGEXP, IN BETWEEN, CASE, WHEN, THEN, ELSE NOT AND, && XOR OR, || = (assignment), :=
The precedence of =
depends on whether it is
used as a comparison operator
(=
) or as an
assignment operator
(=
). When
used as a comparison operator, it has the same precedence as
<=>
,
>=
,
>
,
<=
,
<
,
<>
,
!=
,
IS
,
LIKE
,
REGEXP
, and
IN()
. When used as an assignment
operator, it has the same precedence as
:=
.
Section 13.7.4.1, “SET Syntax for Variable Assignment”, and
Section 9.4, “User-Defined Variables”, explain how MySQL determines
which interpretation of =
should apply.
For operators that occur at the same precedence level within an expression, evaluation proceeds left to right, with the exception that assignments evaluate right to left.
The precedence and meaning of some operators depends on the SQL mode:
By default, ||
is a logical OR
operator. With
PIPES_AS_CONCAT
enabled,
||
is string
concatenation, with a precedence between
^
and
the unary operators.
By default, !
has a higher precedence than NOT
. With
HIGH_NOT_PRECEDENCE
enabled, !
and
NOT
have the same precedence.
See Section 5.1.10, “Server SQL Modes”.
The precedence of operators determines the order of evaluation of terms in an expression. To override this order and group terms explicitly, use parentheses. For example:
mysql>SELECT 1+2*3;
-> 7 mysql>SELECT (1+2)*3;
-> 9
Table 12.3 Comparison Operators
Name | Description |
---|---|
> |
Greater than operator |
>= |
Greater than or equal operator |
< |
Less than operator |
<> , != |
Not equal operator |
<= |
Less than or equal operator |
<=> |
NULL-safe equal to operator |
= |
Equal operator |
BETWEEN ... AND ... |
Whether a value is within a range of values |
COALESCE() |
Return the first non-NULL argument |
GREATEST() |
Return the largest argument |
IN() |
Whether a value is within a set of values |
INTERVAL() |
Return the index of the argument that is less than the first argument |
IS |
Test a value against a boolean |
IS NOT |
Test a value against a boolean |
IS NOT NULL |
NOT NULL value test |
IS NULL |
NULL value test |
ISNULL() |
Test whether the argument is NULL |
LEAST() |
Return the smallest argument |
LIKE |
Simple pattern matching |
NOT BETWEEN ... AND ... |
Whether a value is not within a range of values |
NOT IN() |
Whether a value is not within a set of values |
NOT LIKE |
Negation of simple pattern matching |
STRCMP() |
Compare two strings |
Comparison operations result in a value of 1
(TRUE
), 0
(FALSE
), or NULL
. These
operations work for both numbers and strings. Strings are
automatically converted to numbers and numbers to strings as
necessary.
The following relational comparison operators can be used to compare not only scalar operands, but row operands:
= > < >= <= <> !=
The descriptions for those operators later in this section detail how they work with row operands. For additional examples of row comparisons in the context of row subqueries, see Section 13.2.10.5, “Row Subqueries”.
Some of the functions in this section return values other than
1
(TRUE
),
0
(FALSE
), or
NULL
. LEAST()
and GREATEST()
are examples of
such functions; Section 12.2, “Type Conversion in Expression Evaluation”, describes the
rules for comparison operations performed by these and similar
functions for determining their return values.
To convert a value to a specific type for comparison purposes,
you can use the CAST()
function.
String values can be converted to a different character set
using CONVERT()
. See
Section 12.10, “Cast Functions and Operators”.
By default, string comparisons are not case-sensitive and use
the current character set. The default is
latin1
(cp1252 West European), which also
works well for English.
Equal:
mysql>SELECT 1 = 0;
-> 0 mysql>SELECT '0' = 0;
-> 1 mysql>SELECT '0.0' = 0;
-> 1 mysql>SELECT '0.01' = 0;
-> 0 mysql>SELECT '.01' = 0.01;
-> 1
For row comparisons, (a, b) = (x, y)
is
equivalent to:
(a = x) AND (b = y)
NULL
-safe equal. This operator performs
an equality comparison like the
=
operator,
but returns 1
rather than
NULL
if both operands are
NULL
, and 0
rather
than NULL
if one operand is
NULL
.
The
<=>
operator is equivalent to the standard SQL IS NOT
DISTINCT FROM
operator.
mysql>SELECT 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
-> 1, 1, 0 mysql>SELECT 1 = 1, NULL = NULL, 1 = NULL;
-> 1, NULL, NULL
For row comparisons, (a, b) <=> (x,
y)
is equivalent to:
(a <=> x) AND (b <=> y)
Not equal:
mysql>SELECT '.01' <> '0.01';
-> 1 mysql>SELECT .01 <> '0.01';
-> 0 mysql>SELECT 'zapp' <> 'zappp';
-> 1
For row comparisons, (a, b) <> (x,
y)
and (a, b) != (x, y)
are
equivalent to:
(a <> x) OR (b <> y)
Less than or equal:
mysql> SELECT 0.1 <= 2;
-> 1
For row comparisons, (a, b) <= (x, y)
is equivalent to:
(a < x) OR ((a = x) AND (b <= y))
Less than:
mysql> SELECT 2 < 2;
-> 0
For row comparisons, (a, b) < (x, y)
is equivalent to:
(a < x) OR ((a = x) AND (b < y))
Greater than or equal:
mysql> SELECT 2 >= 2;
-> 1
For row comparisons, (a, b) >= (x, y)
is equivalent to:
(a > x) OR ((a = x) AND (b >= y))
Greater than:
mysql> SELECT 2 > 2;
-> 0
For row comparisons, (a, b) > (x, y)
is equivalent to:
(a > x) OR ((a = x) AND (b > y))
If expr
is greater than or equal
to min
and
expr
is less than or equal to
max
,
BETWEEN
returns
1
, otherwise it returns
0
. This is equivalent to the expression
(
if all the
arguments are of the same type. Otherwise type conversion
takes place according to the rules described in
Section 12.2, “Type Conversion in Expression Evaluation”, but applied to all the
three arguments.
min
<=
expr
AND
expr
<=
max
)
mysql>SELECT 2 BETWEEN 1 AND 3, 2 BETWEEN 3 and 1;
-> 1, 0 mysql>SELECT 1 BETWEEN 2 AND 3;
-> 0 mysql>SELECT 'b' BETWEEN 'a' AND 'c';
-> 1 mysql>SELECT 2 BETWEEN 2 AND '3';
-> 1 mysql>SELECT 2 BETWEEN 2 AND 'x-3';
-> 0
For best results when using
BETWEEN
with date or time
values, use CAST()
to
explicitly convert the values to the desired data type.
Examples: If you compare a
DATETIME
to two
DATE
values, convert the
DATE
values to
DATETIME
values. If you use a
string constant such as '2001-1-1'
in a
comparison to a DATE
, cast
the string to a DATE
.
This is the same as NOT
(
.
expr
BETWEEN
min
AND
max
)
Returns the first non-NULL
value in the
list, or NULL
if there are no
non-NULL
values.
The return type of COALESCE()
is the aggregated type of the argument types.
mysql>SELECT COALESCE(NULL,1);
-> 1 mysql>SELECT COALESCE(NULL,NULL,NULL);
-> NULL
With two or more arguments, returns the largest
(maximum-valued) argument. The arguments are compared using
the same rules as for
LEAST()
.
mysql>SELECT GREATEST(2,0);
-> 2 mysql>SELECT GREATEST(34.0,3.0,5.0,767.0);
-> 767.0 mysql>SELECT GREATEST('B','A','C');
-> 'C'
GREATEST()
returns
NULL
if any argument is
NULL
.
Returns 1
(true) if
expr
is equal to any of the
values in the IN()
list, else returns
0
(false).
Type conversion takes place according to the rules described
in Section 12.2, “Type Conversion in Expression Evaluation”, applied to all the
arguments. If no type conversion is needed for the values in
the IN()
list, they are all constants of
the same type, and expr
can be
compared to each of them as a value of the same type
(possibly after type conversion), an optimization takes
place. The values the list are sorted and the search for
expr
is done using a binary
search, which makes the IN()
operation
very quick.
mysql>SELECT 2 IN (0,3,5,7);
-> 0 mysql>SELECT 'wefwf' IN ('wee','wefwf','weg');
-> 1
IN()
can be used to compare row
constructors:
mysql>SELECT (3,4) IN ((1,2), (3,4));
-> 1 mysql>SELECT (3,4) IN ((1,2), (3,5));
-> 0
You should never mix quoted and unquoted values in an
IN()
list because the comparison rules
for quoted values (such as strings) and unquoted values
(such as numbers) differ. Mixing types may therefore lead to
inconsistent results. For example, do not write an
IN()
expression like this:
SELECT val1 FROM tbl1 WHERE val1 IN (1,2,'a');
Instead, write it like this:
SELECT val1 FROM tbl1 WHERE val1 IN ('1','2','a');
Implicit type conversion may produce nonintuitive results:
mysql> SELECT 'a' IN (0), 0 IN ('b');
-> 1, 1
In both cases, the comparison values are converted to floating-point values, yielding 0.0 in each case, and a comparison result of 1 (true).
The number of values in the IN()
list is
only limited by the
max_allowed_packet
value.
To comply with the SQL standard, IN()
returns NULL
not only if the expression
on the left hand side is NULL
, but also
if no match is found in the list and one of the expressions
in the list is NULL
.
IN()
syntax can also be used to write
certain types of subqueries. See
Section 13.2.10.3, “Subqueries with ANY, IN, or SOME”.
This is the same as NOT
(
.
expr
IN
(value
,...))
Returns 0
if N
< N1
, 1
if
N
<
N2
and so on or
-1
if N
is
NULL
. All arguments are treated as
integers. It is required that N1
< N2
<
N3
< ...
< Nn
for this function to work
correctly. This is because a binary search is used (very
fast).
mysql>SELECT INTERVAL(23, 1, 15, 17, 30, 44, 200);
-> 3 mysql>SELECT INTERVAL(10, 1, 10, 100, 1000);
-> 2 mysql>SELECT INTERVAL(22, 23, 30, 44, 200);
-> 0
Tests a value against a boolean value, where
boolean_value
can be
TRUE
, FALSE
, or
UNKNOWN
.
mysql> SELECT 1 IS TRUE, 0 IS FALSE, NULL IS UNKNOWN;
-> 1, 1, 1
Tests a value against a boolean value, where
boolean_value
can be
TRUE
, FALSE
, or
UNKNOWN
.
mysql> SELECT 1 IS NOT UNKNOWN, 0 IS NOT UNKNOWN, NULL IS NOT UNKNOWN;
-> 1, 1, 0
Tests whether a value is NULL
.
mysql> SELECT 1 IS NULL, 0 IS NULL, NULL IS NULL;
-> 0, 0, 1
To work well with ODBC programs, MySQL supports the
following extra features when using IS
NULL
:
If sql_auto_is_null
variable is set to 1, then after a statement that
successfully inserts an automatically generated
AUTO_INCREMENT
value, you can find
that value by issuing a statement of the following form:
SELECT * FROMtbl_name
WHEREauto_col
IS NULL
If the statement returns a row, the value returned is
the same as if you invoked the
LAST_INSERT_ID()
function. For details, including the return value after
a multiple-row insert, see
Section 12.15, “Information Functions”. If no
AUTO_INCREMENT
value was successfully
inserted, the SELECT
statement returns no row.
The behavior of retrieving an
AUTO_INCREMENT
value by using an
IS NULL
comparison can be
disabled by setting
sql_auto_is_null = 0
.
See Section 5.1.7, “Server System Variables”.
The default value of
sql_auto_is_null
is 0.
For DATE
and
DATETIME
columns that are
declared as NOT NULL
, you can find
the special date '0000-00-00'
by
using a statement like this:
SELECT * FROMtbl_name
WHEREdate_column
IS NULL
This is needed to get some ODBC applications to work
because ODBC does not support a
'0000-00-00'
date value.
See
Obtaining Auto-Increment Values,
and the description for the
FLAG_AUTO_IS_NULL
option at
Connector/ODBC Connection Parameters.
Tests whether a value is not NULL
.
mysql> SELECT 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL;
-> 1, 1, 0
If expr
is
NULL
,
ISNULL()
returns
1
, otherwise it returns
0
.
mysql>SELECT ISNULL(1+1);
-> 0 mysql>SELECT ISNULL(1/0);
-> 1
ISNULL()
can be used instead
of =
to test
whether a value is NULL
. (Comparing a
value to NULL
using
=
always
yields NULL
.)
The ISNULL()
function shares
some special behaviors with the
IS NULL
comparison operator. See the description of
IS NULL
.
With two or more arguments, returns the smallest (minimum-valued) argument. The arguments are compared using the following rules:
If any argument is NULL
, the result
is NULL
. No comparison is needed.
If all arguments are integer-valued, they are compared as integers.
If at least one argument is double precision, they are
compared as double-precision values. Otherwise, if at
least one argument is a
DECIMAL
value, they are
compared as DECIMAL
values.
If the arguments comprise a mix of numbers and strings, they are compared as numbers.
If any argument is a nonbinary (character) string, the arguments are compared as nonbinary strings.
In all other cases, the arguments are compared as binary strings.
The return type of LEAST()
is
the aggregated type of the comparison argument types.
mysql>SELECT LEAST(2,0);
-> 0 mysql>SELECT LEAST(34.0,3.0,5.0,767.0);
-> 3.0 mysql>SELECT LEAST('B','A','C');
-> 'A'
In SQL, all logical operators evaluate to
TRUE
, FALSE
, or
NULL
(UNKNOWN
). In MySQL,
these are implemented as 1 (TRUE
), 0
(FALSE
), and NULL
. Most of
this is common to different SQL database servers, although some
servers may return any nonzero value for
TRUE
.
MySQL evaluates any nonzero, non-NULL
value
to TRUE
. For example, the following
statements all assess to TRUE
:
mysql>SELECT 10 IS TRUE;
-> 1 mysql>SELECT -10 IS TRUE;
-> 1 mysql>SELECT 'string' IS NOT NULL;
-> 1
Logical NOT. Evaluates to 1
if the
operand is 0
, to 0
if
the operand is nonzero, and NOT NULL
returns NULL
.
mysql>SELECT NOT 10;
-> 0 mysql>SELECT NOT 0;
-> 1 mysql>SELECT NOT NULL;
-> NULL mysql>SELECT ! (1+1);
-> 0 mysql>SELECT ! 1+1;
-> 1
The last example produces 1
because the
expression evaluates the same way as
(!1)+1
.
Logical AND. Evaluates to 1
if all
operands are nonzero and not NULL
, to
0
if one or more operands are
0
, otherwise NULL
is
returned.
mysql>SELECT 1 AND 1;
-> 1 mysql>SELECT 1 AND 0;
-> 0 mysql>SELECT 1 AND NULL;
-> NULL mysql>SELECT 0 AND NULL;
-> 0 mysql>SELECT NULL AND 0;
-> 0
Logical OR. When both operands are
non-NULL
, the result is
1
if any operand is nonzero, and
0
otherwise. With a
NULL
operand, the result is
1
if the other operand is nonzero, and
NULL
otherwise. If both operands are
NULL
, the result is
NULL
.
mysql>SELECT 1 OR 1;
-> 1 mysql>SELECT 1 OR 0;
-> 1 mysql>SELECT 0 OR 0;
-> 0 mysql>SELECT 0 OR NULL;
-> NULL mysql>SELECT 1 OR NULL;
-> 1
If the PIPES_AS_CONCAT
SQL mode is enabled,
||
signifies
the SQL-standard string concatenation operator (like
CONCAT()
).
Logical XOR. Returns NULL
if either
operand is NULL
. For
non-NULL
operands, evaluates to
1
if an odd number of operands is
nonzero, otherwise 0
is returned.
mysql>SELECT 1 XOR 1;
-> 0 mysql>SELECT 1 XOR 0;
-> 1 mysql>SELECT 1 XOR NULL;
-> NULL mysql>SELECT 1 XOR 1 XOR 1;
-> 1
a XOR b
is mathematically equal to
(a AND (NOT b)) OR ((NOT a) and b)
.
Assignment operator. Causes the user variable on the left
hand side of the operator to take on the value to its right.
The value on the right hand side may be a literal value,
another variable storing a value, or any legal expression
that yields a scalar value, including the result of a query
(provided that this value is a scalar value). You can
perform multiple assignments in the same
SET
statement. You can perform multiple assignments in the same
statement.
Unlike
=
, the
:=
operator is never interpreted as a comparison operator. This
means you can use
:=
in
any valid SQL statement (not just in
SET
statements) to assign a value to a variable.
mysql>SELECT @var1, @var2;
-> NULL, NULL mysql>SELECT @var1 := 1, @var2;
-> 1, NULL mysql>SELECT @var1, @var2;
-> 1, NULL mysql>SELECT @var1, @var2 := @var1;
-> 1, 1 mysql>SELECT @var1, @var2;
-> 1, 1 mysql>SELECT @var1:=COUNT(*) FROM t1;
-> 4 mysql>SELECT @var1;
-> 4
You can make value assignments using
:=
in
other statements besides
SELECT
, such as
UPDATE
, as shown here:
mysql>SELECT @var1;
-> 4 mysql>SELECT * FROM t1;
-> 1, 3, 5, 7 mysql>UPDATE t1 SET c1 = 2 WHERE c1 = @var1:= 1;
Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql>SELECT @var1;
-> 1 mysql>SELECT * FROM t1;
-> 2, 3, 5, 7
While it is also possible both to set and to read the value
of the same variable in a single SQL statement using the
:=
operator, this is not recommended.
Section 9.4, “User-Defined Variables”, explains why you should
avoid doing this.
This operator is used to perform value assignments in two cases, described in the next two paragraphs.
Within a
SET
statement, =
is treated as an assignment
operator that causes the user variable on the left hand side
of the operator to take on the value to its right. (In other
words, when used in a
SET
statement, =
is treated identically to
:=
.)
The value on the right hand side may be a literal value,
another variable storing a value, or any legal expression
that yields a scalar value, including the result of a query
(provided that this value is a scalar value). You can
perform multiple assignments in the same
SET
statement.
In the SET
clause of an
UPDATE
statement,
=
also acts as an assignment operator; in
this case, however, it causes the column named on the left
hand side of the operator to assume the value given to the
right, provided any WHERE
conditions that
are part of the UPDATE
are
met. You can make multiple assignments in the same
SET
clause of an
UPDATE
statement.
In any other context, =
is treated as a
comparison operator.
mysql>SELECT @var1, @var2;
-> NULL, NULL mysql>SELECT @var1 := 1, @var2;
-> 1, NULL mysql>SELECT @var1, @var2;
-> 1, NULL mysql>SELECT @var1, @var2 := @var1;
-> 1, 1 mysql>SELECT @var1, @var2;
-> 1, 1
For more information, see Section 13.7.4.1, “SET Syntax for Variable Assignment”, Section 13.2.11, “UPDATE Statement”, and Section 13.2.10, “Subqueries”.
CASE
value
WHEN
[compare_value
] THEN
result
[WHEN
[compare_value
] THEN
result
...] [ELSE
result
] END
CASE WHEN
[
condition
] THEN
result
[WHEN
[condition
] THEN
result
...] [ELSE
result
] END
The first CASE
syntax returns the
result
for the first
comparison that is true. The second syntax returns the result
for the first condition that is true. If no comparison or
condition is true, the result after value
=compare_value
ELSE
is
returned, or NULL
if there is no
ELSE
part.
The syntax of the CASE
expr described here differs slightly
from that of the SQL CASE
statement described in
Section 13.6.5.1, “CASE Statement”, for use inside stored programs. The
CASE
statement cannot have an
ELSE NULL
clause, and it is terminated
with END CASE
instead of
END
.
The return type of a CASE
expression result is the aggregated type of all result values.
mysql>SELECT CASE 1 WHEN 1 THEN 'one'
->WHEN 2 THEN 'two' ELSE 'more' END;
-> 'one' mysql>SELECT CASE WHEN 1>0 THEN 'true' ELSE 'false' END;
-> 'true' mysql>SELECT CASE BINARY 'B'
->WHEN 'a' THEN 1 WHEN 'b' THEN 2 END;
-> NULL
If expr1
is TRUE
(
and expr1
<>
0
), expr1
<> NULLIF()
returns expr2
. Otherwise, it
returns expr3
.
There is also an IF
statement, which differs from the
IF()
function described here. See
Section 13.6.5.2, “IF Statement”.
If only one of expr2
or
expr3
is explicitly
NULL
, the result type of the
IF()
function is the type of
the non-NULL
expression.
The default return type of IF()
(which may matter when it is stored into a temporary table) is
calculated as follows:
If expr2
or
expr3
produce a string, the
result is a string.
If expr2
and
expr3
are both strings, the
result is case-sensitive if either string is
case-sensitive.
If expr2
or
expr3
produce a floating-point
value, the result is a floating-point value.
If expr2
or
expr3
produce an integer, the
result is an integer.
mysql>SELECT IF(1>2,2,3);
-> 3 mysql>SELECT IF(1<2,'yes','no');
-> 'yes' mysql>SELECT IF(STRCMP('test','test1'),'no','yes');
-> 'no'
If expr1
is not
NULL
,
IFNULL()
returns
expr1
; otherwise it returns
expr2
.
mysql>SELECT IFNULL(1,0);
-> 1 mysql>SELECT IFNULL(NULL,10);
-> 10 mysql>SELECT IFNULL(1/0,10);
-> 10 mysql>SELECT IFNULL(1/0,'yes');
-> 'yes'
The default return type of
IFNULL(
is the more “general” of the two expressions, in
the order expr1
,expr2
)STRING
, REAL
,
or INTEGER
. Consider the case of a table
based on expressions or where MySQL must internally store a
value returned by IFNULL()
in a
temporary table:
mysql>CREATE TABLE tmp SELECT IFNULL(1,'test') AS test;
mysql>DESCRIBE tmp;
+-------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+--------------+------+-----+---------+-------+ | test | varbinary(4) | NO | | | | +-------+--------------+------+-----+---------+-------+
In this example, the type of the test
column is VARBINARY(4)
(a
string type).
Returns NULL
if
is true, otherwise
returns expr1
=
expr2
expr1
. This is the same as
CASE WHEN
.
expr1
=
expr2
THEN NULL ELSE
expr1
END
The return value has the same type as the first argument.
mysql>SELECT NULLIF(1,1);
-> NULL mysql>SELECT NULLIF(1,2);
-> 1
MySQL evaluates expr1
twice if
the arguments are not equal.
Table 12.7 Numeric Functions and Operators
Name | Description |
---|---|
% , MOD |
Modulo operator |
* |
Multiplication operator |
+ |
Addition operator |
- |
Minus operator |
- |
Change the sign of the argument |
/ |
Division operator |
ABS() |
Return the absolute value |
ACOS() |
Return the arc cosine |
ASIN() |
Return the arc sine |
ATAN() |
Return the arc tangent |
ATAN2() , ATAN() |
Return the arc tangent of the two arguments |
CEIL() |
Return the smallest integer value not less than the argument |
CEILING() |
Return the smallest integer value not less than the argument |
CONV() |
Convert numbers between different number bases |
COS() |
Return the cosine |
COT() |
Return the cotangent |
CRC32() |
Compute a cyclic redundancy check value |
DEGREES() |
Convert radians to degrees |
DIV |
Integer division |
EXP() |
Raise to the power of |
FLOOR() |
Return the largest integer value not greater than the argument |
LN() |
Return the natural logarithm of the argument |
LOG() |
Return the natural logarithm of the first argument |
LOG10() |
Return the base-10 logarithm of the argument |
LOG2() |
Return the base-2 logarithm of the argument |
MOD() |
Return the remainder |
PI() |
Return the value of pi |
POW() |
Return the argument raised to the specified power |
POWER() |
Return the argument raised to the specified power |
RADIANS() |
Return argument converted to radians |
RAND() |
Return a random floating-point value |
ROUND() |
Round the argument |
SIGN() |
Return the sign of the argument |
SIN() |
Return the sine of the argument |
SQRT() |
Return the square root of the argument |
TAN() |
Return the tangent of the argument |
TRUNCATE() |
Truncate to specified number of decimal places |
The usual arithmetic operators are available. The result is determined according to the following rules:
In the case of
-
,
+
, and
*
, the result
is calculated with BIGINT
(64-bit) precision if both operands are integers.
If both operands are integers and any of them are unsigned,
the result is an unsigned integer. For subtraction, if the
NO_UNSIGNED_SUBTRACTION
SQL mode is enabled, the result is signed even if any
operand is unsigned.
If any of the operands of a
+
,
-
,
/
,
*
,
%
is a real or
string value, the precision of the result is the precision
of the operand with the maximum precision.
In division performed with
/
, the scale
of the result when using two exact-value operands is the
scale of the first operand plus the value of the
div_precision_increment
system variable (which is 4 by default). For example, the
result of the expression 5.05 / 0.014
has
a scale of six decimal places
(360.714286
).
These rules are applied for each operation, such that nested
calculations imply the precision of each component. Hence,
(14620 / 9432456) / (24250 / 9432456)
,
resolves first to (0.0014) / (0.0026)
, with
the final result having 8 decimal places
(0.60288653
).
Because of these rules and the way they are applied, care should be taken to ensure that components and subcomponents of a calculation use the appropriate level of precision. See Section 12.10, “Cast Functions and Operators”.
For information about handling of overflow in numeric expression evaluation, see Section 11.1.7, “Out-of-Range and Overflow Handling”.
Arithmetic operators apply to numbers. For other types of
values, alternative operations may be available. For example, to
add date values, use DATE_ADD()
;
see Section 12.6, “Date and Time Functions”.
Addition:
mysql> SELECT 3+5;
-> 8
Subtraction:
mysql> SELECT 3-5;
-> -2
Unary minus. This operator changes the sign of the operand.
mysql> SELECT - 2;
-> -2
Multiplication:
mysql>SELECT 3*5;
-> 15 mysql>SELECT 18014398509481984*18014398509481984.0;
-> 324518553658426726783156020576256.0 mysql>SELECT 18014398509481984*18014398509481984;
-> out-of-range error
The last expression produces an error because the result of
the integer multiplication exceeds the 64-bit range of
BIGINT
calculations. (See
Section 11.1, “Numeric Data Types”.)
Division:
mysql> SELECT 3/5;
-> 0.60
Division by zero produces a NULL
result:
mysql> SELECT 102/(1-1);
-> NULL
A division is calculated with
BIGINT
arithmetic only if
performed in a context where its result is converted to an
integer.
Integer division. Discards from the division result any fractional part to the right of the decimal point.
If either operand has a noninteger type, the operands are
converted to DECIMAL
and
divided using DECIMAL
arithmetic before converting the result to
BIGINT
. If the result exceeds
BIGINT
range, an error occurs.
mysql> SELECT 5 DIV 2, -5 DIV 2, 5 DIV -2, -5 DIV -2;
-> 2, -2, -2, 2
Modulo operation. Returns the remainder of
N
divided by
M
. For more information, see the
description for the MOD()
function in Section 12.5.2, “Mathematical Functions”.
Table 12.9 Mathematical Functions
Name | Description |
---|---|
ABS() |
Return the absolute value |
ACOS() |
Return the arc cosine |
ASIN() |
Return the arc sine |
ATAN() |
Return the arc tangent |
ATAN2() , ATAN() |
Return the arc tangent of the two arguments |
CEIL() |
Return the smallest integer value not less than the argument |
CEILING() |
Return the smallest integer value not less than the argument |
CONV() |
Convert numbers between different number bases |
COS() |
Return the cosine |
COT() |
Return the cotangent |
CRC32() |
Compute a cyclic redundancy check value |
DEGREES() |
Convert radians to degrees |
EXP() |
Raise to the power of |
FLOOR() |
Return the largest integer value not greater than the argument |
LN() |
Return the natural logarithm of the argument |
LOG() |
Return the natural logarithm of the first argument |
LOG10() |
Return the base-10 logarithm of the argument |
LOG2() |
Return the base-2 logarithm of the argument |
MOD() |
Return the remainder |
PI() |
Return the value of pi |
POW() |
Return the argument raised to the specified power |
POWER() |
Return the argument raised to the specified power |
RADIANS() |
Return argument converted to radians |
RAND() |
Return a random floating-point value |
ROUND() |
Round the argument |
SIGN() |
Return the sign of the argument |
SIN() |
Return the sine of the argument |
SQRT() |
Return the square root of the argument |
TAN() |
Return the tangent of the argument |
TRUNCATE() |
Truncate to specified number of decimal places |
All mathematical functions return NULL
in the
event of an error.
Returns the absolute value of X
.
mysql>SELECT ABS(2);
-> 2 mysql>SELECT ABS(-32);
-> 32
This function is safe to use with
BIGINT
values.
Returns the arc cosine of X
, that
is, the value whose cosine is X
.
Returns NULL
if
X
is not in the range
-1
to 1
.
mysql>SELECT ACOS(1);
-> 0 mysql>SELECT ACOS(1.0001);
-> NULL mysql>SELECT ACOS(0);
-> 1.5707963267949
Returns the arc sine of X
, that
is, the value whose sine is X
.
Returns NULL
if
X
is not in the range
-1
to 1
.
mysql>SELECT ASIN(0.2);
-> 0.20135792079033 mysql>SELECT ASIN('foo');
+-------------+ | ASIN('foo') | +-------------+ | 0 | +-------------+ 1 row in set, 1 warning (0.00 sec) mysql>SHOW WARNINGS;
+---------+------+-----------------------------------------+ | Level | Code | Message | +---------+------+-----------------------------------------+ | Warning | 1292 | Truncated incorrect DOUBLE value: 'foo' | +---------+------+-----------------------------------------+
Returns the arc tangent of X
,
that is, the value whose tangent is
X
.
mysql>SELECT ATAN(2);
-> 1.1071487177941 mysql>SELECT ATAN(-2);
-> -1.1071487177941
Returns the arc tangent of the two variables
X
and
Y
. It is similar to calculating
the arc tangent of
, except that the
signs of both arguments are used to determine the quadrant
of the result.
Y
/
X
mysql>SELECT ATAN(-2,2);
-> -0.78539816339745 mysql>SELECT ATAN2(PI(),0);
-> 1.5707963267949
Returns the smallest integer value not less than
X
.
mysql>SELECT CEILING(1.23);
-> 2 mysql>SELECT CEILING(-1.23);
-> -1
For exact-value numeric arguments, the return value has an exact-value numeric type. For string or floating-point arguments, the return value has a floating-point type.
Converts numbers between different number bases. Returns a
string representation of the number
N
, converted from base
from_base
to base
to_base
. Returns
NULL
if any argument is
NULL
. The argument
N
is interpreted as an integer,
but may be specified as an integer or a string. The minimum
base is 2
and the maximum base is
36
. If
from_base
is a negative number,
N
is regarded as a signed number.
Otherwise, N
is treated as
unsigned. CONV()
works with
64-bit precision.
mysql>SELECT CONV('a',16,2);
-> '1010' mysql>SELECT CONV('6E',18,8);
-> '172' mysql>SELECT CONV(-17,10,-18);
-> '-H' mysql>SELECT CONV(10+'10'+'10'+X'0a',10,10);
-> '40'
Returns the cosine of X
, where
X
is given in radians.
mysql> SELECT COS(PI());
-> -1
Returns the cotangent of X
.
mysql>SELECT COT(12);
-> -1.5726734063977 mysql>SELECT COT(0);
-> out-of-range error
Computes a cyclic redundancy check value and returns a
32-bit unsigned value. The result is NULL
if the argument is NULL
. The argument is
expected to be a string and (if possible) is treated as one
if it is not.
mysql>SELECT CRC32('MySQL');
-> 3259397556 mysql>SELECT CRC32('mysql');
-> 2501908538
Returns the argument X
, converted
from radians to degrees.
mysql>SELECT DEGREES(PI());
-> 180 mysql>SELECT DEGREES(PI() / 2);
-> 90
Returns the value of e (the base of
natural logarithms) raised to the power of
X
. The inverse of this function
is LOG()
(using a single
argument only) or LN()
.
mysql>SELECT EXP(2);
-> 7.3890560989307 mysql>SELECT EXP(-2);
-> 0.13533528323661 mysql>SELECT EXP(0);
-> 1
Returns the largest integer value not greater than
X
.
mysql> SELECT FLOOR(1.23), FLOOR(-1.23);
-> 1, -2
For exact-value numeric arguments, the return value has an exact-value numeric type. For string or floating-point arguments, the return value has a floating-point type.
Formats the number X
to a format
like '#,###,###.##'
, rounded to
D
decimal places, and returns the
result as a string. For details, see
Section 12.7, “String Functions and Operators”.
This function can be used to obtain a hexadecimal representation of a decimal number or a string; the manner in which it does so varies according to the argument's type. See this function's description in Section 12.7, “String Functions and Operators”, for details.
Returns the natural logarithm of
X
; that is, the
base-e logarithm of
X
. If
X
is less than or equal to 0.0E0,
the function returns NULL
and a warning
“Invalid argument for logarithm” is reported.
mysql>SELECT LN(2);
-> 0.69314718055995 mysql>SELECT LN(-2);
-> NULL
This function is synonymous with
LOG(
.
The inverse of this function is the
X
)EXP()
function.
If called with one parameter, this function returns the
natural logarithm of X
. If
X
is less than or equal to 0.0E0,
the function returns NULL
and a warning
“Invalid argument for logarithm” is reported.
The inverse of this function (when called with a single
argument) is the EXP()
function.
mysql>SELECT LOG(2);
-> 0.69314718055995 mysql>SELECT LOG(-2);
-> NULL
If called with two parameters, this function returns the
logarithm of X
to the base
B
. If
X
is less than or equal to 0, or
if B
is less than or equal to 1,
then NULL
is returned.
mysql>SELECT LOG(2,65536);
-> 16 mysql>SELECT LOG(10,100);
-> 2 mysql>SELECT LOG(1,100);
-> NULL
LOG(
is equivalent to
B
,X
)LOG(
.
X
) /
LOG(B
)
Returns the base-2 logarithm of
. If
X
X
is less than or equal to 0.0E0,
the function returns NULL
and a warning
“Invalid argument for logarithm” is reported.
mysql>SELECT LOG2(65536);
-> 16 mysql>SELECT LOG2(-100);
-> NULL
LOG2()
is useful for finding
out how many bits a number requires for storage. This
function is equivalent to the expression
LOG(
.
X
) /
LOG(2)
Returns the base-10 logarithm of
X
. If
X
is less than or equal to 0.0E0,
the function returns NULL
and a warning
“Invalid argument for logarithm” is reported.
mysql>SELECT LOG10(2);
-> 0.30102999566398 mysql>SELECT LOG10(100);
-> 2 mysql>SELECT LOG10(-100);
-> NULL
Modulo operation. Returns the remainder of
N
divided by
M
.
mysql>SELECT MOD(234, 10);
-> 4 mysql>SELECT 253 % 7;
-> 1 mysql>SELECT MOD(29,9);
-> 2 mysql>SELECT 29 MOD 9;
-> 2
This function is safe to use with
BIGINT
values.
MOD()
also works on values
that have a fractional part and returns the exact remainder
after division:
mysql> SELECT MOD(34.5,3);
-> 1.5
MOD(
returns N
,0)NULL
.
Returns the value of π (pi). The default number of decimal places displayed is seven, but MySQL uses the full double-precision value internally.
mysql>SELECT PI();
-> 3.141593 mysql>SELECT PI()+0.000000000000000000;
-> 3.141592653589793116
Returns the value of X
raised to
the power of Y
.
mysql>SELECT POW(2,2);
-> 4 mysql>SELECT POW(2,-2);
-> 0.25
This is a synonym for POW()
.
Returns the argument X
, converted
from degrees to radians. (Note that π radians equals 180
degrees.)
mysql> SELECT RADIANS(90);
-> 1.5707963267949
Returns a random floating-point value
v
in the range
0
<= v
<
1.0
. To obtain a random integer
R
in the range
i
<=
R
<
j
, use the expression
FLOOR(
− i
+ RAND() * (j
.
For example, to obtain a random integer in the range the
range i
))7
<=
R
< 12
, use
the following statement:
SELECT FLOOR(7 + (RAND() * 5));
If an integer argument N
is
specified, it is used as the seed value:
With a constant initializer argument, the seed is initialized once when the statement is prepared, prior to execution.
With a nonconstant initializer argument (such as a
column name), the seed is initialized with the value for
each invocation of
RAND()
.
One implication of this behavior is that for equal argument
values,
RAND(
returns the same value each time, and thus produces a
repeatable sequence of column values. In the following
example, the sequence of values produced by
N
)RAND(3)
is the same both places it
occurs.
mysql>CREATE TABLE t (i INT);
Query OK, 0 rows affected (0.42 sec) mysql>INSERT INTO t VALUES(1),(2),(3);
Query OK, 3 rows affected (0.00 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql>SELECT i, RAND() FROM t;
+------+------------------+ | i | RAND() | +------+------------------+ | 1 | 0.61914388706828 | | 2 | 0.93845168309142 | | 3 | 0.83482678498591 | +------+------------------+ 3 rows in set (0.00 sec) mysql>SELECT i, RAND(3) FROM t;
+------+------------------+ | i | RAND(3) | +------+------------------+ | 1 | 0.90576975597606 | | 2 | 0.37307905813035 | | 3 | 0.14808605345719 | +------+------------------+ 3 rows in set (0.00 sec) mysql>SELECT i, RAND() FROM t;
+------+------------------+ | i | RAND() | +------+------------------+ | 1 | 0.35877890638893 | | 2 | 0.28941420772058 | | 3 | 0.37073435016976 | +------+------------------+ 3 rows in set (0.00 sec) mysql>SELECT i, RAND(3) FROM t;
+------+------------------+ | i | RAND(3) | +------+------------------+ | 1 | 0.90576975597606 | | 2 | 0.37307905813035 | | 3 | 0.14808605345719 | +------+------------------+ 3 rows in set (0.01 sec)
RAND()
in a
WHERE
clause is evaluated for every row
(when selecting from one table) or combination of rows (when
selecting from a multiple-table join). Thus, for optimizer
purposes, RAND()
is not a
constant value and cannot be used for index optimizations.
For more information, see
Section 8.2.1.18, “Function Call Optimization”.
Use of a column with RAND()
values in an ORDER BY
or GROUP
BY
clause may yield unexpected results because for
either clause a RAND()
expression can be evaluated multiple times for the same row,
each time returning a different result. If the goal is to
retrieve rows in random order, you can use a statement like
this:
SELECT * FROM tbl_name
ORDER BY RAND();
To select a random sample from a set of rows, combine
ORDER BY RAND()
with
LIMIT
:
SELECT * FROM table1, table2 WHERE a=b AND c<d ORDER BY RAND() LIMIT 1000;
RAND()
is not meant to be a
perfect random generator. It is a fast way to generate
random numbers on demand that is portable between platforms
for the same MySQL version.
This function is unsafe for statement-based replication. A
warning is logged if you use this function when
binlog_format
is set to
STATEMENT
.
Rounds the argument X
to
D
decimal places. The rounding
algorithm depends on the data type of
X
. D
defaults to 0 if not specified. D
can be negative to cause D
digits
left of the decimal point of the value
X
to become zero.
mysql>SELECT ROUND(-1.23);
-> -1 mysql>SELECT ROUND(-1.58);
-> -2 mysql>SELECT ROUND(1.58);
-> 2 mysql>SELECT ROUND(1.298, 1);
-> 1.3 mysql>SELECT ROUND(1.298, 0);
-> 1 mysql>SELECT ROUND(23.298, -1);
-> 20
The return value has the same type as the first argument (assuming that it is integer, double, or decimal). This means that for an integer argument, the result is an integer (no decimal places):
mysql> SELECT ROUND(150.000,2), ROUND(150,2);
+------------------+--------------+
| ROUND(150.000,2) | ROUND(150,2) |
+------------------+--------------+
| 150.00 | 150 |
+------------------+--------------+
ROUND()
uses the following
rules depending on the type of the first argument:
For exact-value numbers,
ROUND()
uses the
“round half away from zero” or “round
toward nearest” rule: A value with a fractional
part of .5 or greater is rounded up to the next integer
if positive or down to the next integer if negative. (In
other words, it is rounded away from zero.) A value with
a fractional part less than .5 is rounded down to the
next integer if positive or up to the next integer if
negative.
For approximate-value numbers, the result depends on the
C library. On many systems, this means that
ROUND()
uses the
“round to nearest even” rule: A value with
a fractional part exactly half way between two integers
is rounded to the nearest even integer.
The following example shows how rounding differs for exact and approximate values:
mysql> SELECT ROUND(2.5), ROUND(25E-1);
+------------+--------------+
| ROUND(2.5) | ROUND(25E-1) |
+------------+--------------+
| 3 | 2 |
+------------+--------------+
For more information, see Section 12.22, “Precision Math”.
Returns the sign of the argument as -1
,
0
, or 1
, depending on
whether X
is negative, zero, or
positive.
mysql>SELECT SIGN(-32);
-> -1 mysql>SELECT SIGN(0);
-> 0 mysql>SELECT SIGN(234);
-> 1
Returns the sine of X
, where
X
is given in radians.
mysql>SELECT SIN(PI());
-> 1.2246063538224e-16 mysql>SELECT ROUND(SIN(PI()));
-> 0
Returns the square root of a nonnegative number
X
.
mysql>SELECT SQRT(4);
-> 2 mysql>SELECT SQRT(20);
-> 4.4721359549996 mysql>SELECT SQRT(-16);
-> NULL
Returns the tangent of X
, where
X
is given in radians.
mysql>SELECT TAN(PI());
-> -1.2246063538224e-16 mysql>SELECT TAN(PI()+1);
-> 1.5574077246549
Returns the number X
, truncated
to D
decimal places. If
D
is 0
, the
result has no decimal point or fractional part.
D
can be negative to cause
D
digits left of the decimal
point of the value X
to become
zero.
mysql>SELECT TRUNCATE(1.223,1);
-> 1.2 mysql>SELECT TRUNCATE(1.999,1);
-> 1.9 mysql>SELECT TRUNCATE(1.999,0);
-> 1 mysql>SELECT TRUNCATE(-1.999,1);
-> -1.9 mysql>SELECT TRUNCATE(122,-2);
-> 100 mysql>SELECT TRUNCATE(10.28*100,0);
-> 1028
All numbers are rounded toward zero.
This section describes the functions that can be used to manipulate temporal values. See Section 11.2, “Date and Time Data Types”, for a description of the range of values each date and time type has and the valid formats in which values may be specified.
Table 12.10 Date and Time Functions
Name | Description |
---|---|
ADDDATE() |
Add time values (intervals) to a date value |
ADDTIME() |
Add time |
CONVERT_TZ() |
Convert from one time zone to another |
CURDATE() |
Return the current date |
CURRENT_DATE() , CURRENT_DATE |
Synonyms for CURDATE() |
CURRENT_TIME() , CURRENT_TIME |
Synonyms for CURTIME() |
CURRENT_TIMESTAMP() , CURRENT_TIMESTAMP |
Synonyms for NOW() |
CURTIME() |
Return the current time |
DATE() |
Extract the date part of a date or datetime expression |
DATE_ADD() |
Add time values (intervals) to a date value |
DATE_FORMAT() |
Format date as specified |
DATE_SUB() |
Subtract a time value (interval) from a date |
DATEDIFF() |
Subtract two dates |
DAY() |
Synonym for DAYOFMONTH() |
DAYNAME() |
Return the name of the weekday |
DAYOFMONTH() |
Return the day of the month (0-31) |
DAYOFWEEK() |
Return the weekday index of the argument |
DAYOFYEAR() |
Return the day of the year (1-366) |
EXTRACT() |
Extract part of a date |
FROM_DAYS() |
Convert a day number to a date |
FROM_UNIXTIME() |
Format Unix timestamp as a date |
GET_FORMAT() |
Return a date format string |
HOUR() |
Extract the hour |
LAST_DAY |
Return the last day of the month for the argument |
LOCALTIME() , LOCALTIME |
Synonym for NOW() |
LOCALTIMESTAMP , LOCALTIMESTAMP() |
Synonym for NOW() |
MAKEDATE() |
Create a date from the year and day of year |
MAKETIME() |
Create time from hour, minute, second |
MICROSECOND() |
Return the microseconds from argument |
MINUTE() |
Return the minute from the argument |
MONTH() |
Return the month from the date passed |
MONTHNAME() |
Return the name of the month |
NOW() |
Return the current date and time |
PERIOD_ADD() |
Add a period to a year-month |
PERIOD_DIFF() |
Return the number of months between periods |
QUARTER() |
Return the quarter from a date argument |
SEC_TO_TIME() |
Converts seconds to 'hh:mm:ss' format |
SECOND() |
Return the second (0-59) |
STR_TO_DATE() |
Convert a string to a date |
SUBDATE() |
Synonym for DATE_SUB() when invoked with three arguments |
SUBTIME() |
Subtract times |
SYSDATE() |
Return the time at which the function executes |
TIME() |
Extract the time portion of the expression passed |
TIME_FORMAT() |
Format as time |
TIME_TO_SEC() |
Return the argument converted to seconds |
TIMEDIFF() |
Subtract time |
TIMESTAMP() |
With a single argument, this function returns the date or datetime expression; with two arguments, the sum of the arguments |
TIMESTAMPADD() |
Add an interval to a datetime expression |
TIMESTAMPDIFF() |
Subtract an interval from a datetime expression |
TO_DAYS() |
Return the date argument converted to days |
TO_SECONDS() |
Return the date or datetime argument converted to seconds since Year 0 |
UNIX_TIMESTAMP() |
Return a Unix timestamp |
UTC_DATE() |
Return the current UTC date |
UTC_TIME() |
Return the current UTC time |
UTC_TIMESTAMP() |
Return the current UTC date and time |
WEEK() |
Return the week number |
WEEKDAY() |
Return the weekday index |
WEEKOFYEAR() |
Return the calendar week of the date (1-53) |
YEAR() |
Return the year |
YEARWEEK() |
Return the year and week |
Here is an example that uses date functions. The following query
selects all rows with a date_col
value
from within the last 30 days:
mysql>SELECT
->something
FROMtbl_name
WHERE DATE_SUB(CURDATE(),INTERVAL 30 DAY) <=
date_col
;
The query also selects rows with dates that lie in the future.
Functions that expect date values usually accept datetime values and ignore the time part. Functions that expect time values usually accept datetime values and ignore the date part.
Functions that return the current date or time each are evaluated
only once per query at the start of query execution. This means
that multiple references to a function such as
NOW()
within a single query always
produce the same result. (For our purposes, a single query also
includes a call to a stored program (stored routine, trigger, or
event) and all subprograms called by that program.) This principle
also applies to CURDATE()
,
CURTIME()
,
UTC_DATE()
,
UTC_TIME()
,
UTC_TIMESTAMP()
, and to any of
their synonyms.
The CURRENT_TIMESTAMP()
,
CURRENT_TIME()
,
CURRENT_DATE()
, and
FROM_UNIXTIME()
functions return
values in the current session time zone, which is available as the
session value of the time_zone
system variable. In addition,
UNIX_TIMESTAMP()
assumes that its
argument is a datetime value in the session time zone. See
Section 5.1.12, “MySQL Server Time Zone Support”.
Some date functions can be used with “zero” dates or
incomplete dates such as '2001-11-00'
, whereas
others cannot. Functions that extract parts of dates typically
work with incomplete dates and thus can return 0 when you might
otherwise expect a nonzero value. For example:
mysql> SELECT DAYOFMONTH('2001-11-00'), MONTH('2005-00-00');
-> 0, 0
Other functions expect complete dates and return
NULL
for incomplete dates. These include
functions that perform date arithmetic or that map parts of dates
to names. For example:
mysql>SELECT DATE_ADD('2006-05-00',INTERVAL 1 DAY);
-> NULL mysql>SELECT DAYNAME('2006-05-00');
-> NULL
Several functions are strict when passed a
DATE()
function value as their
argument and reject incomplete dates with a day part of zero:
CONVERT_TZ()
,
DATE_ADD()
,
DATE_SUB()
,
DAYOFYEAR()
,
TIMESTAMPDIFF()
,
TO_DAYS()
,
TO_SECONDS()
,
WEEK()
,
WEEKDAY()
,
WEEKOFYEAR()
,
YEARWEEK()
.
Fractional seconds for TIME
,
DATETIME
, and TIMESTAMP
values are supported, with up to microsecond precision. Functions
that take temporal arguments accept values with fractional
seconds. Return values from temporal functions include fractional
seconds as appropriate.
ADDDATE(
,
date
,INTERVAL
expr
unit
)ADDDATE(
expr
,days
)
When invoked with the INTERVAL
form of the
second argument, ADDDATE()
is a
synonym for DATE_ADD()
. The
related function SUBDATE()
is a
synonym for DATE_SUB()
. For
information on the INTERVAL
unit
argument, see
Temporal Intervals.
mysql>SELECT DATE_ADD('2008-01-02', INTERVAL 31 DAY);
-> '2008-02-02' mysql>SELECT ADDDATE('2008-01-02', INTERVAL 31 DAY);
-> '2008-02-02'
When invoked with the days
form of
the second argument, MySQL treats it as an integer number of
days to be added to expr
.
mysql> SELECT ADDDATE('2008-01-02', 31);
-> '2008-02-02'
ADDTIME()
adds
expr2
to
expr1
and returns the result.
expr1
is a time or datetime
expression, and expr2
is a time
expression.
mysql>SELECT ADDTIME('2007-12-31 23:59:59.999999', '1 1:1:1.000002');
-> '2008-01-02 01:01:01.000001' mysql>SELECT ADDTIME('01:00:00.999999', '02:00:00.999998');
-> '03:00:01.999997'
CONVERT_TZ()
converts a
datetime value dt
from the time
zone given by from_tz
to the time
zone given by to_tz
and returns the
resulting value. Time zones are specified as described in
Section 5.1.12, “MySQL Server Time Zone Support”. This function returns
NULL
if the arguments are invalid.
If the value falls out of the supported range of the
TIMESTAMP
type when converted
from from_tz
to UTC, no conversion
occurs. The TIMESTAMP
range is
described in Section 11.2.1, “Date and Time Data Type Syntax”.
mysql>SELECT CONVERT_TZ('2004-01-01 12:00:00','GMT','MET');
-> '2004-01-01 13:00:00' mysql>SELECT CONVERT_TZ('2004-01-01 12:00:00','+00:00','+10:00');
-> '2004-01-01 22:00:00'
To use named time zones such as 'MET'
or
'Europe/Amsterdam'
, the time zone tables
must be properly set up. For instructions, see
Section 5.1.12, “MySQL Server Time Zone Support”.
Returns the current date as a value in
'
or
YYYY-MM-DD
'YYYYMMDD
format, depending on
whether the function is used in string or numeric context.
mysql>SELECT CURDATE();
-> '2008-06-13' mysql>SELECT CURDATE() + 0;
-> 20080613
CURRENT_DATE
and
CURRENT_DATE()
are synonyms for
CURDATE()
.
CURRENT_TIME
,
CURRENT_TIME([
fsp
])
CURRENT_TIME
and
CURRENT_TIME()
are synonyms for
CURTIME()
.
CURRENT_TIMESTAMP
,
CURRENT_TIMESTAMP([
fsp
])
CURRENT_TIMESTAMP
and
CURRENT_TIMESTAMP()
are
synonyms for NOW()
.
Returns the current time as a value in
'hh:mm:ss'
or
hhmmss
format, depending on whether
the function is used in string or numeric context. The value
is expressed in the session time zone.
If the fsp
argument is given to
specify a fractional seconds precision from 0 to 6, the return
value includes a fractional seconds part of that many digits.
mysql>SELECT CURTIME();
-> '23:50:26' mysql>SELECT CURTIME() + 0;
-> 235026.000000
Extracts the date part of the date or datetime expression
expr
.
mysql> SELECT DATE('2003-12-31 01:02:03');
-> '2003-12-31'
DATEDIFF()
returns
expr1
−
expr2
expressed as a value in days
from one date to the other. expr1
and expr2
are date or date-and-time
expressions. Only the date parts of the values are used in the
calculation.
mysql>SELECT DATEDIFF('2007-12-31 23:59:59','2007-12-30');
-> 1 mysql>SELECT DATEDIFF('2010-11-30 23:59:59','2010-12-31');
-> -31
DATE_ADD(
,
date
,INTERVAL
expr
unit
)DATE_SUB(
date
,INTERVAL
expr
unit
)
These functions perform date arithmetic. The
date
argument specifies the
starting date or datetime value.
expr
is an expression specifying
the interval value to be added or subtracted from the starting
date. expr
is evaluated as a
string; it may start with a -
for negative
intervals. unit
is a keyword
indicating the units in which the expression should be
interpreted.
For more information about temporal interval syntax, including
a full list of unit
specifiers, the
expected form of the expr
argument
for each unit
value, and rules for
operand interpretation in temporal arithmetic, see
Temporal Intervals.
The return value depends on the arguments:
DATE
if the
date
argument is a
DATE
value and your
calculations involve only YEAR
,
MONTH
, and DAY
parts
(that is, no time parts).
DATETIME
if the first
argument is a DATETIME
(or
TIMESTAMP
) value, or if the
first argument is a DATE
and the unit
value uses
HOURS
, MINUTES
, or
SECONDS
.
String otherwise.
To ensure that the result is
DATETIME
, you can use
CAST()
to convert the first
argument to DATETIME
.
mysql>SELECT DATE_ADD('2018-05-01',INTERVAL 1 DAY);
-> '2018-05-02' mysql>SELECT DATE_SUB('2018-05-01',INTERVAL 1 YEAR);
-> '2017-05-01' mysql>SELECT DATE_ADD('2020-12-31 23:59:59',
->INTERVAL 1 SECOND);
-> '2021-01-01 00:00:00' mysql>SELECT DATE_ADD('2018-12-31 23:59:59',
->INTERVAL 1 DAY);
-> '2019-01-01 23:59:59' mysql>SELECT DATE_ADD('2100-12-31 23:59:59',
->INTERVAL '1:1' MINUTE_SECOND);
-> '2101-01-01 00:01:00' mysql>SELECT DATE_SUB('2025-01-01 00:00:00',
->INTERVAL '1 1:1:1' DAY_SECOND);
-> '2024-12-30 22:58:59' mysql>SELECT DATE_ADD('1900-01-01 00:00:00',
->INTERVAL '-1 10' DAY_HOUR);
-> '1899-12-30 14:00:00' mysql>SELECT DATE_SUB('1998-01-02', INTERVAL 31 DAY);
-> '1997-12-02' mysql>SELECT DATE_ADD('1992-12-31 23:59:59.000002',
->INTERVAL '1.999999' SECOND_MICROSECOND);
-> '1993-01-01 00:00:01.000001'
Formats the date
value according to
the format
string.
The specifiers shown in the following table may be used in the
format
string. The
%
character is required before format
specifier characters. The specifiers apply to other functions
as well: STR_TO_DATE()
,
TIME_FORMAT()
,
UNIX_TIMESTAMP()
.
Specifier | Description |
---|---|
%a |
Abbreviated weekday name
(Sun ..Sat ) |
%b |
Abbreviated month name (Jan ..Dec ) |
%c |
Month, numeric (0 ..12 ) |
%D |
Day of the month with English suffix (0th ,
1st , 2nd ,
3rd , …) |
%d |
Day of the month, numeric (00 ..31 ) |
%e |
Day of the month, numeric (0 ..31 ) |
%f |
Microseconds (000000 ..999999 ) |
%H |
Hour (00 ..23 ) |
%h |
Hour (01 ..12 ) |
%I |
Hour (01 ..12 ) |
%i |
Minutes, numeric (00 ..59 ) |
%j |
Day of year (001 ..366 ) |
%k |
Hour (0 ..23 ) |
%l |
Hour (1 ..12 ) |
%M |
Month name (January ..December ) |
%m |
Month, numeric (00 ..12 ) |
%p |
AM or PM |
%r |
Time, 12-hour (hh:mm:ss followed by
AM or PM ) |
%S |
Seconds (00 ..59 ) |
%s |
Seconds (00 ..59 ) |
%T |
Time, 24-hour (hh:mm:ss ) |
%U |
Week (00 ..53 ), where Sunday is the
first day of the week;
WEEK() mode 0 |
%u |
Week (00 ..53 ), where Monday is the
first day of the week;
WEEK() mode 1 |
%V |
Week (01 ..53 ), where Sunday is the
first day of the week;
WEEK() mode 2; used with
%X |
%v |
Week (01 ..53 ), where Monday is the
first day of the week;
WEEK() mode 3; used with
%x |
%W |
Weekday name (Sunday ..Saturday ) |
%w |
Day of the week
(0 =Sunday..6 =Saturday) |
%X |
Year for the week where Sunday is the first day of the week, numeric,
four digits; used with %V |
%x |
Year for the week, where Monday is the first day of the week, numeric,
four digits; used with %v |
%Y |
Year, numeric, four digits |
%y |
Year, numeric (two digits) |
%% |
A literal % character |
% |
x , for any
“x ” not listed
above |
Ranges for the month and day specifiers begin with zero due to
the fact that MySQL permits the storing of incomplete dates
such as '2014-00-00'
.
The language used for day and month names and abbreviations is
controlled by the value of the
lc_time_names
system variable
(Section 10.16, “MySQL Server Locale Support”).
For the %U
, %u
,
%V
, and %v
specifiers,
see the description of the
WEEK()
function for information
about the mode values. The mode affects how week numbering
occurs.
DATE_FORMAT()
returns a string
with a character set and collation given by
character_set_connection
and
collation_connection
so that
it can return month and weekday names containing non-ASCII
characters.
mysql>SELECT DATE_FORMAT('2009-10-04 22:23:00', '%W %M %Y');
-> 'Sunday October 2009' mysql>SELECT DATE_FORMAT('2007-10-04 22:23:00', '%H:%i:%s');
-> '22:23:00' mysql>SELECT DATE_FORMAT('1900-10-04 22:23:00',
->'%D %y %a %d %m %b %j');
-> '4th 00 Thu 04 10 Oct 277' mysql>SELECT DATE_FORMAT('1997-10-04 22:23:00',
->'%H %k %I %r %T %S %w');
-> '22 22 10 10:23:00 PM 22:23:00 00 6' mysql>SELECT DATE_FORMAT('1999-01-01', '%X %V');
-> '1998 52' mysql>SELECT DATE_FORMAT('2006-06-00', '%d');
-> '00'
DATE_SUB(
date
,INTERVAL
expr
unit
)
See the description for
DATE_ADD()
.
DAY()
is a synonym for
DAYOFMONTH()
.
Returns the name of the weekday for
date
. The language used for the
name is controlled by the value of the
lc_time_names
system variable
(Section 10.16, “MySQL Server Locale Support”).
mysql> SELECT DAYNAME('2007-02-03');
-> 'Saturday'
Returns the day of the month for
date
, in the range
1
to 31
, or
0
for dates such as
'0000-00-00'
or
'2008-00-00'
that have a zero day part.
mysql> SELECT DAYOFMONTH('2007-02-03');
-> 3
Returns the weekday index for date
(1
= Sunday, 2
= Monday,
…, 7
= Saturday). These index values
correspond to the ODBC standard.
mysql> SELECT DAYOFWEEK('2007-02-03');
-> 7
Returns the day of the year for
date
, in the range
1
to 366
.
mysql> SELECT DAYOFYEAR('2007-02-03');
-> 34
The EXTRACT()
function uses the
same kinds of unit
specifiers as
DATE_ADD()
or
DATE_SUB()
, but extracts parts
from the date rather than performing date arithmetic. For
information on the unit
argument,
see Temporal Intervals.
mysql>SELECT EXTRACT(YEAR FROM '2019-07-02');
-> 2019 mysql>SELECT EXTRACT(YEAR_MONTH FROM '2019-07-02 01:02:03');
-> 201907 mysql>SELECT EXTRACT(DAY_MINUTE FROM '2019-07-02 01:02:03');
-> 20102 mysql>SELECT EXTRACT(MICROSECOND
->FROM '2003-01-02 10:30:00.000123');
-> 123
Given a day number N
, returns a
DATE
value.
mysql> SELECT FROM_DAYS(730669);
-> '2000-07-03'
Use FROM_DAYS()
with caution on
old dates. It is not intended for use with values that precede
the advent of the Gregorian calendar (1582). See
Section 12.8, “What Calendar Is Used By MySQL?”.
FROM_UNIXTIME(
unix_timestamp
[,format
])
Returns a representation of the
unix_timestamp
argument as a value
in '
or
YYYY-MM-DD
hh:mm:ss
'YYYYMMDDhhmmss
format, depending on
whether the function is used in a string or numeric context.
unix_timestamp
is an internal
timestamp value representing seconds since
'1970-01-01 00:00:00'
UTC, such as produced
by the UNIX_TIMESTAMP()
function.
The return value is expressed in the session time zone.
(Clients can set the session time zone as described in
Section 5.1.12, “MySQL Server Time Zone Support”.) The
format
string, if given, is used to
format the result the same way as described in the entry for
the DATE_FORMAT()
function.
mysql>SELECT FROM_UNIXTIME(1447430881);
-> '2015-11-13 10:08:01' mysql>SELECT FROM_UNIXTIME(1447430881) + 0;
-> 20151113100801 mysql>SELECT FROM_UNIXTIME(1447430881,
->'%Y %D %M %h:%i:%s %x');
-> '2015 13th November 10:08:01 2015'
If you use UNIX_TIMESTAMP()
and FROM_UNIXTIME()
to
convert between values in a non-UTC time zone and Unix
timestamp values, the conversion is lossy because the
mapping is not one-to-one in both directions. For details,
see the description of the
UNIX_TIMESTAMP()
function.
GET_FORMAT({DATE|TIME|DATETIME},
{'EUR'|'USA'|'JIS'|'ISO'|'INTERNAL'})
Returns a format string. This function is useful in
combination with the
DATE_FORMAT()
and the
STR_TO_DATE()
functions.
The possible values for the first and second arguments result
in several possible format strings (for the specifiers used,
see the table in the
DATE_FORMAT()
function
description). ISO format refers to ISO 9075, not ISO 8601.
Function Call | Result |
---|---|
GET_FORMAT(DATE,'USA') |
'%m.%d.%Y' |
GET_FORMAT(DATE,'JIS') |
'%Y-%m-%d' |
GET_FORMAT(DATE,'ISO') |
'%Y-%m-%d' |
GET_FORMAT(DATE,'EUR') |
'%d.%m.%Y' |
GET_FORMAT(DATE,'INTERNAL') |
'%Y%m%d' |
GET_FORMAT(DATETIME,'USA') |
'%Y-%m-%d %H.%i.%s' |
GET_FORMAT(DATETIME,'JIS') |
'%Y-%m-%d %H:%i:%s' |
GET_FORMAT(DATETIME,'ISO') |
'%Y-%m-%d %H:%i:%s' |
GET_FORMAT(DATETIME,'EUR') |
'%Y-%m-%d %H.%i.%s' |
GET_FORMAT(DATETIME,'INTERNAL') |
'%Y%m%d%H%i%s' |
GET_FORMAT(TIME,'USA') |
'%h:%i:%s %p' |
GET_FORMAT(TIME,'JIS') |
'%H:%i:%s' |
GET_FORMAT(TIME,'ISO') |
'%H:%i:%s' |
GET_FORMAT(TIME,'EUR') |
'%H.%i.%s' |
GET_FORMAT(TIME,'INTERNAL') |
'%H%i%s' |
TIMESTAMP
can also be used as
the first argument to
GET_FORMAT()
, in which case the
function returns the same values as for
DATETIME
.
mysql>SELECT DATE_FORMAT('2003-10-03',GET_FORMAT(DATE,'EUR'));
-> '03.10.2003' mysql>SELECT STR_TO_DATE('10.31.2003',GET_FORMAT(DATE,'USA'));
-> '2003-10-31'
Returns the hour for time
. The
range of the return value is 0
to
23
for time-of-day values. However, the
range of TIME
values actually
is much larger, so HOUR
can return values
greater than 23
.
mysql>SELECT HOUR('10:05:03');
-> 10 mysql>SELECT HOUR('272:59:59');
-> 272
Takes a date or datetime value and returns the corresponding
value for the last day of the month. Returns
NULL
if the argument is invalid.
mysql>SELECT LAST_DAY('2003-02-05');
-> '2003-02-28' mysql>SELECT LAST_DAY('2004-02-05');
-> '2004-02-29' mysql>SELECT LAST_DAY('2004-01-01 01:01:01');
-> '2004-01-31' mysql>SELECT LAST_DAY('2003-03-32');
-> NULL
LOCALTIME
and
LOCALTIME()
are synonyms for
NOW()
.
LOCALTIMESTAMP
,
LOCALTIMESTAMP([
fsp
])
LOCALTIMESTAMP
and
LOCALTIMESTAMP()
are synonyms
for NOW()
.
Returns a date, given year and day-of-year values.
dayofyear
must be greater than 0 or
the result is NULL
.
mysql>SELECT MAKEDATE(2011,31), MAKEDATE(2011,32);
-> '2011-01-31', '2011-02-01' mysql>SELECT MAKEDATE(2011,365), MAKEDATE(2014,365);
-> '2011-12-31', '2014-12-31' mysql>SELECT MAKEDATE(2011,0);
-> NULL
Returns a time value calculated from the
hour
,
minute
, and
second
arguments.
The second
argument can have a
fractional part.
mysql> SELECT MAKETIME(12,15,30);
-> '12:15:30'
Returns the microseconds from the time or datetime expression
expr
as a number in the range from
0
to 999999
.
mysql>SELECT MICROSECOND('12:00:00.123456');
-> 123456 mysql>SELECT MICROSECOND('2019-12-31 23:59:59.000010');
-> 10
Returns the minute for time
, in the
range 0
to 59
.
mysql> SELECT MINUTE('2008-02-03 10:05:03');
-> 5
Returns the month for date
, in the
range 1
to 12
for
January to December, or 0
for dates such as
'0000-00-00'
or
'2008-00-00'
that have a zero month part.
mysql> SELECT MONTH('2008-02-03');
-> 2
Returns the full name of the month for
date
. The language used for the
name is controlled by the value of the
lc_time_names
system variable
(Section 10.16, “MySQL Server Locale Support”).
mysql> SELECT MONTHNAME('2008-02-03');
-> 'February'
Returns the current date and time as a value in
'
or
YYYY-MM-DD
hh:mm:ss
'YYYYMMDDhhmmss
format, depending on
whether the function is used in string or numeric context. The
value is expressed in the session time zone.
If the fsp
argument is given to
specify a fractional seconds precision from 0 to 6, the return
value includes a fractional seconds part of that many digits.
mysql>SELECT NOW();
-> '2007-12-15 23:50:26' mysql>SELECT NOW() + 0;
-> 20071215235026.000000
NOW()
returns a constant time
that indicates the time at which the statement began to
execute. (Within a stored function or trigger,
NOW()
returns the time at which
the function or triggering statement began to execute.) This
differs from the behavior for
SYSDATE()
, which returns the
exact time at which it executes.
mysql>SELECT NOW(), SLEEP(2), NOW();
+---------------------+----------+---------------------+ | NOW() | SLEEP(2) | NOW() | +---------------------+----------+---------------------+ | 2006-04-12 13:47:36 | 0 | 2006-04-12 13:47:36 | +---------------------+----------+---------------------+ mysql>SELECT SYSDATE(), SLEEP(2), SYSDATE();
+---------------------+----------+---------------------+ | SYSDATE() | SLEEP(2) | SYSDATE() | +---------------------+----------+---------------------+ | 2006-04-12 13:47:44 | 0 | 2006-04-12 13:47:46 | +---------------------+----------+---------------------+
In addition, the SET TIMESTAMP
statement
affects the value returned by
NOW()
but not by
SYSDATE()
. This means that
timestamp settings in the binary log have no effect on
invocations of SYSDATE()
.
Setting the timestamp to a nonzero value causes each
subsequent invocation of NOW()
to return that value. Setting the timestamp to zero cancels
this effect so that NOW()
once
again returns the current date and time.
See the description for
SYSDATE()
for additional
information about the differences between the two functions.
Adds N
months to period
P
(in the format
YYMM
or
YYYYMM
). Returns a value in the
format YYYYMM
.
The period argument P
is
not a date value.
mysql> SELECT PERIOD_ADD(200801,2);
-> 200803
Returns the number of months between periods
P1
and
P2
. P1
and P2
should be in the format
YYMM
or
YYYYMM
. Note that the period
arguments P1
and
P2
are not
date values.
mysql> SELECT PERIOD_DIFF(200802,200703);
-> 11
Returns the quarter of the year for
date
, in the range
1
to 4
.
mysql> SELECT QUARTER('2008-04-01');
-> 2
Returns the second for time
, in the
range 0
to 59
.
mysql> SELECT SECOND('10:05:03');
-> 3
Returns the seconds
argument,
converted to hours, minutes, and seconds, as a
TIME
value. The range of the
result is constrained to that of the
TIME
data type. A warning
occurs if the argument corresponds to a value outside that
range.
mysql>SELECT SEC_TO_TIME(2378);
-> '00:39:38' mysql>SELECT SEC_TO_TIME(2378) + 0;
-> 3938
This is the inverse of the
DATE_FORMAT()
function. It
takes a string str
and a format
string format
.
STR_TO_DATE()
returns a
DATETIME
value if the format
string contains both date and time parts, or a
DATE
or
TIME
value if the string
contains only date or time parts. If the date, time, or
datetime value extracted from str
is illegal, STR_TO_DATE()
returns NULL
and produces a warning.
The server scans str
attempting to
match format
to it. The format
string can contain literal characters and format specifiers
beginning with %
. Literal characters in
format
must match literally in
str
. Format specifiers in
format
must match a date or time
part in str
. For the specifiers
that can be used in format
, see the
DATE_FORMAT()
function
description.
mysql>SELECT STR_TO_DATE('01,5,2013','%d,%m,%Y');
-> '2013-05-01' mysql>SELECT STR_TO_DATE('May 1, 2013','%M %d,%Y');
-> '2013-05-01'
Scanning starts at the beginning of
str
and fails if
format
is found not to match. Extra
characters at the end of str
are
ignored.
mysql>SELECT STR_TO_DATE('a09:30:17','a%h:%i:%s');
-> '09:30:17' mysql>SELECT STR_TO_DATE('a09:30:17','%h:%i:%s');
-> NULL mysql>SELECT STR_TO_DATE('09:30:17a','%h:%i:%s');
-> '09:30:17'
Unspecified date or time parts have a value of 0, so
incompletely specified values in
str
produce a result with some or
all parts set to 0:
mysql>SELECT STR_TO_DATE('abc','abc');
-> '0000-00-00' mysql>SELECT STR_TO_DATE('9','%m');
-> '0000-09-00' mysql>SELECT STR_TO_DATE('9','%s');
-> '00:00:09'
Range checking on the parts of date values is as described in Section 11.2.2, “The DATE, DATETIME, and TIMESTAMP Types”. This means, for example, that “zero” dates or dates with part values of 0 are permitted unless the SQL mode is set to disallow such values.
mysql>SELECT STR_TO_DATE('00/00/0000', '%m/%d/%Y');
-> '0000-00-00' mysql>SELECT STR_TO_DATE('04/31/2004', '%m/%d/%Y');
-> '2004-04-31'
If the NO_ZERO_DATE
or
NO_ZERO_IN_DATE
SQL mode is
enabled, zero dates or part of dates are disallowed. In that
case, STR_TO_DATE()
returns
NULL
and generates a warning:
mysql>SET sql_mode = '';
mysql>SELECT STR_TO_DATE('15:35:00', '%H:%i:%s');
+-------------------------------------+ | STR_TO_DATE('15:35:00', '%H:%i:%s') | +-------------------------------------+ | 15:35:00 | +-------------------------------------+ mysql>SET sql_mode = 'NO_ZERO_IN_DATE';
mysql>SELECT STR_TO_DATE('15:35:00', '%h:%i:%s');
+-------------------------------------+ | STR_TO_DATE('15:35:00', '%h:%i:%s') | +-------------------------------------+ | NULL | +-------------------------------------+ mysql>SHOW WARNINGS\G
*************************** 1. row *************************** Level: Warning Code: 1411 Message: Incorrect datetime value: '15:35:00' for function str_to_date
You cannot use format "%X%V"
to convert a
year-week string to a date because the combination of a year
and week does not uniquely identify a year and month if the
week crosses a month boundary. To convert a year-week to a
date, you should also specify the weekday:
mysql> SELECT STR_TO_DATE('200442 Monday', '%X%V %W');
-> '2004-10-18'
SUBDATE(
,
date
,INTERVAL
expr
unit
)SUBDATE(
expr
,days
)
When invoked with the INTERVAL
form of the
second argument, SUBDATE()
is a
synonym for DATE_SUB()
. For
information on the INTERVAL
unit
argument, see the discussion
for DATE_ADD()
.
mysql>SELECT DATE_SUB('2008-01-02', INTERVAL 31 DAY);
-> '2007-12-02' mysql>SELECT SUBDATE('2008-01-02', INTERVAL 31 DAY);
-> '2007-12-02'
The second form enables the use of an integer value for
days
. In such cases, it is
interpreted as the number of days to be subtracted from the
date or datetime expression expr
.
mysql> SELECT SUBDATE('2008-01-02 12:00:00', 31);
-> '2007-12-02 12:00:00'
SUBTIME()
returns
expr1
−
expr2
expressed as a value in the
same format as expr1
.
expr1
is a time or datetime
expression, and expr2
is a time
expression.
mysql>SELECT SUBTIME('2007-12-31 23:59:59.999999','1 1:1:1.000002');
-> '2007-12-30 22:58:58.999997' mysql>SELECT SUBTIME('01:00:00.999999', '02:00:00.999998');
-> '-00:59:59.999999'
Returns the current date and time as a value in
'
or
YYYY-MM-DD
hh:mm:ss
'YYYYMMDDhhmmss
format, depending on
whether the function is used in string or numeric context.
If the fsp
argument is given to
specify a fractional seconds precision from 0 to 6, the return
value includes a fractional seconds part of that many digits.
SYSDATE()
returns the time at
which it executes. This differs from the behavior for
NOW()
, which returns a constant
time that indicates the time at which the statement began to
execute. (Within a stored function or trigger,
NOW()
returns the time at which
the function or triggering statement began to execute.)
mysql>SELECT NOW(), SLEEP(2), NOW();
+---------------------+----------+---------------------+ | NOW() | SLEEP(2) | NOW() | +---------------------+----------+---------------------+ | 2006-04-12 13:47:36 | 0 | 2006-04-12 13:47:36 | +---------------------+----------+---------------------+ mysql>SELECT SYSDATE(), SLEEP(2), SYSDATE();
+---------------------+----------+---------------------+ | SYSDATE() | SLEEP(2) | SYSDATE() | +---------------------+----------+---------------------+ | 2006-04-12 13:47:44 | 0 | 2006-04-12 13:47:46 | +---------------------+----------+---------------------+
In addition, the SET TIMESTAMP
statement
affects the value returned by
NOW()
but not by
SYSDATE()
. This means that
timestamp settings in the binary log have no effect on
invocations of SYSDATE()
.
Because SYSDATE()
can return
different values even within the same statement, and is not
affected by SET TIMESTAMP
, it is
nondeterministic and therefore unsafe for replication if
statement-based binary logging is used. If that is a problem,
you can use row-based logging.
Alternatively, you can use the
--sysdate-is-now
option to
cause SYSDATE()
to be an alias
for NOW()
. This works if the
option is used on both the master and the slave.
The nondeterministic nature of
SYSDATE()
also means that
indexes cannot be used for evaluating expressions that refer
to it.
Extracts the time part of the time or datetime expression
expr
and returns it as a string.
This function is unsafe for statement-based replication. A
warning is logged if you use this function when
binlog_format
is set to
STATEMENT
.
mysql>SELECT TIME('2003-12-31 01:02:03');
-> '01:02:03' mysql>SELECT TIME('2003-12-31 01:02:03.000123');
-> '01:02:03.000123'
TIMEDIFF()
returns
expr1
−
expr2
expressed as a time value.
expr1
and
expr2
are time or date-and-time
expressions, but both must be of the same type.
The result returned by TIMEDIFF()
is
limited to the range allowed for
TIME
values. Alternatively, you
can use either of the functions
TIMESTAMPDIFF()
and
UNIX_TIMESTAMP()
, both of which
return integers.
mysql>SELECT TIMEDIFF('2000:01:01 00:00:00',
->'2000:01:01 00:00:00.000001');
-> '-00:00:00.000001' mysql>SELECT TIMEDIFF('2008-12-31 23:59:59.000001',
->'2008-12-30 01:01:01.000002');
-> '46:58:57.999999'
TIMESTAMP(
,
expr
)TIMESTAMP(
expr1
,expr2
)
With a single argument, this function returns the date or
datetime expression expr
as a
datetime value. With two arguments, it adds the time
expression expr2
to the date or
datetime expression expr1
and
returns the result as a datetime value.
mysql>SELECT TIMESTAMP('2003-12-31');
-> '2003-12-31 00:00:00' mysql>SELECT TIMESTAMP('2003-12-31 12:00:00','12:00:00');
-> '2004-01-01 00:00:00'
TIMESTAMPADD(
unit
,interval
,datetime_expr
)
Adds the integer expression
interval
to the date or datetime
expression datetime_expr
. The unit
for interval
is given by the
unit
argument, which should be one
of the following values: MICROSECOND
(microseconds), SECOND
,
MINUTE
, HOUR
,
DAY
, WEEK
,
MONTH
, QUARTER
, or
YEAR
.
The unit
value may be specified
using one of keywords as shown, or with a prefix of
SQL_TSI_
. For example,
DAY
and SQL_TSI_DAY
both
are legal.
mysql>SELECT TIMESTAMPADD(MINUTE,1,'2003-01-02');
-> '2003-01-02 00:01:00' mysql>SELECT TIMESTAMPADD(WEEK,1,'2003-01-02');
-> '2003-01-09'
TIMESTAMPDIFF(
unit
,datetime_expr1
,datetime_expr2
)
Returns datetime_expr2
−
datetime_expr1
, where
datetime_expr1
and
datetime_expr2
are date or datetime
expressions. One expression may be a date and the other a
datetime; a date value is treated as a datetime having the
time part '00:00:00'
where necessary. The
unit for the result (an integer) is given by the
unit
argument. The legal values for
unit
are the same as those listed
in the description of the
TIMESTAMPADD()
function.
mysql>SELECT TIMESTAMPDIFF(MONTH,'2003-02-01','2003-05-01');
-> 3 mysql>SELECT TIMESTAMPDIFF(YEAR,'2002-05-01','2001-01-01');
-> -1 mysql>SELECT TIMESTAMPDIFF(MINUTE,'2003-02-01','2003-05-01 12:05:55');
-> 128885
The order of the date or datetime arguments for this
function is the opposite of that used with the
TIMESTAMP()
function when
invoked with 2 arguments.
This is used like the
DATE_FORMAT()
function, but the
format
string may contain format
specifiers only for hours, minutes, seconds, and microseconds.
Other specifiers produce a NULL
value or
0
.
If the time
value contains an hour
part that is greater than 23
, the
%H
and %k
hour format
specifiers produce a value larger than the usual range of
0..23
. The other hour format specifiers
produce the hour value modulo 12.
mysql> SELECT TIME_FORMAT('100:00:00', '%H %k %h %I %l');
-> '100 100 04 04 4'
Returns the time
argument,
converted to seconds.
mysql>SELECT TIME_TO_SEC('22:23:00');
-> 80580 mysql>SELECT TIME_TO_SEC('00:39:38');
-> 2378
Given a date date
, returns a day
number (the number of days since year 0).
mysql>SELECT TO_DAYS(950501);
-> 728779 mysql>SELECT TO_DAYS('2007-10-07');
-> 733321
TO_DAYS()
is not intended for
use with values that precede the advent of the Gregorian
calendar (1582), because it does not take into account the
days that were lost when the calendar was changed. For dates
before 1582 (and possibly a later year in other locales),
results from this function are not reliable. See
Section 12.8, “What Calendar Is Used By MySQL?”, for details.
Remember that MySQL converts two-digit year values in dates to
four-digit form using the rules in
Section 11.2, “Date and Time Data Types”. For example,
'2008-10-07'
and
'08-10-07'
are seen as identical dates:
mysql> SELECT TO_DAYS('2008-10-07'), TO_DAYS('08-10-07');
-> 733687, 733687
In MySQL, the zero date is defined as
'0000-00-00'
, even though this date is
itself considered invalid. This means that, for
'0000-00-00'
and
'0000-01-01'
,
TO_DAYS()
returns the values
shown here:
mysql>SELECT TO_DAYS('0000-00-00');
+-----------------------+ | to_days('0000-00-00') | +-----------------------+ | NULL | +-----------------------+ 1 row in set, 1 warning (0.00 sec) mysql>SHOW WARNINGS;
+---------+------+----------------------------------------+ | Level | Code | Message | +---------+------+----------------------------------------+ | Warning | 1292 | Incorrect datetime value: '0000-00-00' | +---------+------+----------------------------------------+ 1 row in set (0.00 sec) mysql>SELECT TO_DAYS('0000-01-01');
+-----------------------+ | to_days('0000-01-01') | +-----------------------+ | 1 | +-----------------------+ 1 row in set (0.00 sec)
This is true whether or not the
ALLOW_INVALID_DATES
SQL
server mode is enabled.
Given a date or datetime expr
,
returns the number of seconds since the year 0. If
expr
is not a valid date or
datetime value, returns NULL
.
mysql>SELECT TO_SECONDS(950501);
-> 62966505600 mysql>SELECT TO_SECONDS('2009-11-29');
-> 63426672000 mysql>SELECT TO_SECONDS('2009-11-29 13:43:32');
-> 63426721412 mysql>SELECT TO_SECONDS( NOW() );
-> 63426721458
Like TO_DAYS()
,
TO_SECONDS()
is not intended for use with
values that precede the advent of the Gregorian calendar
(1582), because it does not take into account the days that
were lost when the calendar was changed. For dates before 1582
(and possibly a later year in other locales), results from
this function are not reliable. See
Section 12.8, “What Calendar Is Used By MySQL?”, for details.
Like TO_DAYS()
,
TO_SECONDS()
, converts two-digit year
values in dates to four-digit form using the rules in
Section 11.2, “Date and Time Data Types”.
In MySQL, the zero date is defined as
'0000-00-00'
, even though this date is
itself considered invalid. This means that, for
'0000-00-00'
and
'0000-01-01'
,
TO_SECONDS()
returns the values
shown here:
mysql>SELECT TO_SECONDS('0000-00-00');
+--------------------------+ | TO_SECONDS('0000-00-00') | +--------------------------+ | NULL | +--------------------------+ 1 row in set, 1 warning (0.00 sec) mysql>SHOW WARNINGS;
+---------+------+----------------------------------------+ | Level | Code | Message | +---------+------+----------------------------------------+ | Warning | 1292 | Incorrect datetime value: '0000-00-00' | +---------+------+----------------------------------------+ 1 row in set (0.00 sec) mysql>SELECT TO_SECONDS('0000-01-01');
+--------------------------+ | TO_SECONDS('0000-01-01') | +--------------------------+ | 86400 | +--------------------------+ 1 row in set (0.00 sec)
This is true whether or not the
ALLOW_INVALID_DATES
SQL
server mode is enabled.
If UNIX_TIMESTAMP()
is called
with no date
argument, it returns a
Unix timestamp representing seconds since '1970-01-01
00:00:00'
UTC.
If UNIX_TIMESTAMP()
is called
with a date
argument, it returns
the value of the argument as seconds since
'1970-01-01 00:00:00'
UTC. The server
interprets date
as a value in the
session time zone and converts it to an internal Unix
timestamp value in UTC. (Clients can set the session time zone
as described in Section 5.1.12, “MySQL Server Time Zone Support”.) The
date
argument may be a
DATE
,
DATETIME
, or
TIMESTAMP
string, or a number
in YYMMDD
,
YYMMDDhhmmss
,
YYYYMMDD
, or
YYYYMMDDhhmmss
format. If the
argument includes a time part, it may optionally include a
fractional seconds part.
The return value is an integer if no argument is given or the
argument does not include a fractional seconds part, or
DECIMAL
if an argument is given
that includes a fractional seconds part.
When the date
argument is a
TIMESTAMP
column,
UNIX_TIMESTAMP()
returns the
internal timestamp value directly, with no implicit
“string-to-Unix-timestamp” conversion.
The valid range of argument values is the same as for the
TIMESTAMP
data type:
'1970-01-01 00:00:01.000000'
UTC to
'2038-01-19 03:14:07.999999'
UTC. If you
pass an out-of-range date to
UNIX_TIMESTAMP()
, it returns
0
.
mysql>SELECT UNIX_TIMESTAMP();
-> 1447431666 mysql>SELECT UNIX_TIMESTAMP('2015-11-13 10:20:19');
-> 1447431619 mysql>SELECT UNIX_TIMESTAMP('2015-11-13 10:20:19.012');
-> 1447431619.012
If you use UNIX_TIMESTAMP()
and
FROM_UNIXTIME()
to convert
between values in a non-UTC time zone and Unix timestamp
values, the conversion is lossy because the mapping is not
one-to-one in both directions. For example, due to conventions
for local time zone changes such as Daylight Saving Time
(DST), it is possible for
UNIX_TIMESTAMP()
to map two
values that are distinct in a non-UTC time zone to the same
Unix timestamp value.
FROM_UNIXTIME()
will map that
value back to only one of the original values. Here is an
example, using values that are distinct in the
MET
time zone:
mysql>SET time_zone = 'MET';
mysql>SELECT UNIX_TIMESTAMP('2005-03-27 03:00:00');
+---------------------------------------+ | UNIX_TIMESTAMP('2005-03-27 03:00:00') | +---------------------------------------+ | 1111885200 | +---------------------------------------+ mysql>SELECT UNIX_TIMESTAMP('2005-03-27 02:00:00');
+---------------------------------------+ | UNIX_TIMESTAMP('2005-03-27 02:00:00') | +---------------------------------------+ | 1111885200 | +---------------------------------------+ mysql>SELECT FROM_UNIXTIME(1111885200);
+---------------------------+ | FROM_UNIXTIME(1111885200) | +---------------------------+ | 2005-03-27 03:00:00 | +---------------------------+
To use named time zones such as 'MET'
or
'Europe/Amsterdam'
, the time zone tables
must be properly set up. For instructions, see
Section 5.1.12, “MySQL Server Time Zone Support”.
If you want to subtract
UNIX_TIMESTAMP()
columns, you
might want to cast them to signed integers. See
Section 12.10, “Cast Functions and Operators”.
Returns the current UTC date as a value in
'
or
YYYY-MM-DD
'YYYYMMDD
format, depending on
whether the function is used in string or numeric context.
mysql> SELECT UTC_DATE(), UTC_DATE() + 0;
-> '2003-08-14', 20030814
Returns the current UTC time as a value in
'hh:mm:ss'
or
hhmmss
format, depending on whether
the function is used in string or numeric context.
If the fsp
argument is given to
specify a fractional seconds precision from 0 to 6, the return
value includes a fractional seconds part of that many digits.
mysql> SELECT UTC_TIME(), UTC_TIME() + 0;
-> '18:07:53', 180753.000000
UTC_TIMESTAMP
,
UTC_TIMESTAMP([
fsp
])
Returns the current UTC date and time as a value in
'
or
YYYY-MM-DD
hh:mm:ss
'YYYYMMDDhhmmss
format, depending on
whether the function is used in string or numeric context.
If the fsp
argument is given to
specify a fractional seconds precision from 0 to 6, the return
value includes a fractional seconds part of that many digits.
mysql> SELECT UTC_TIMESTAMP(), UTC_TIMESTAMP() + 0;
-> '2003-08-14 18:08:04', 20030814180804.000000
This function returns the week number for
date
. The two-argument form of
WEEK()
enables you to specify
whether the week starts on Sunday or Monday and whether the
return value should be in the range from 0
to 53
or from 1
to
53
. If the mode
argument is omitted, the value of the
default_week_format
system
variable is used. See
Section 5.1.7, “Server System Variables”.
The following table describes how the
mode
argument works.
Mode | First day of week | Range | Week 1 is the first week … |
---|---|---|---|
0 | Sunday | 0-53 | with a Sunday in this year |
1 | Monday | 0-53 | with 4 or more days this year |
2 | Sunday | 1-53 | with a Sunday in this year |
3 | Monday | 1-53 | with 4 or more days this year |
4 | Sunday | 0-53 | with 4 or more days this year |
5 | Monday | 0-53 | with a Monday in this year |
6 | Sunday | 1-53 | with 4 or more days this year |
7 | Monday | 1-53 | with a Monday in this year |
For mode
values with a meaning of
“with 4 or more days this year,” weeks are
numbered according to ISO 8601:1988:
If the week containing January 1 has 4 or more days in the new year, it is week 1.
Otherwise, it is the last week of the previous year, and the next week is week 1.
mysql>SELECT WEEK('2008-02-20');
-> 7 mysql>SELECT WEEK('2008-02-20',0);
-> 7 mysql>SELECT WEEK('2008-02-20',1);
-> 8 mysql>SELECT WEEK('2008-12-31',1);
-> 53
If a date falls in the last week of the previous year, MySQL
returns 0
if you do not use
2
, 3
,
6
, or 7
as the optional
mode
argument:
mysql> SELECT YEAR('2000-01-01'), WEEK('2000-01-01',0);
-> 2000, 0
One might argue that WEEK()
should return 52
because the given date
actually occurs in the 52nd week of 1999.
WEEK()
returns
0
instead so that the return value is
“the week number in the given year.” This makes
use of the WEEK()
function
reliable when combined with other functions that extract a
date part from a date.
If you prefer a result evaluated with respect to the year that
contains the first day of the week for the given date, use
0
, 2
,
5
, or 7
as the optional
mode
argument.
mysql> SELECT WEEK('2000-01-01',2);
-> 52
Alternatively, use the
YEARWEEK()
function:
mysql>SELECT YEARWEEK('2000-01-01');
-> 199952 mysql>SELECT MID(YEARWEEK('2000-01-01'),5,2);
-> '52'
Returns the weekday index for date
(0
= Monday, 1
=
Tuesday, … 6
= Sunday).
mysql>SELECT WEEKDAY('2008-02-03 22:23:00');
-> 6 mysql>SELECT WEEKDAY('2007-11-06');
-> 1
Returns the calendar week of the date as a number in the range
from 1
to 53
.
WEEKOFYEAR()
is a compatibility
function that is equivalent to
WEEK(
.
date
,3)
mysql> SELECT WEEKOFYEAR('2008-02-20');
-> 8
Returns the year for date
, in the
range 1000
to 9999
, or
0
for the “zero” date.
mysql> SELECT YEAR('1987-01-01');
-> 1987
YEARWEEK(
,
date
)YEARWEEK(
date
,mode
)
Returns year and week for a date. The year in the result may be different from the year in the date argument for the first and the last week of the year.
The mode
argument works exactly
like the mode
argument to
WEEK()
. For the single-argument
syntax, a mode
value of 0 is used.
Unlike WEEK()
, the value of
default_week_format
does not
influence YEARWEEK()
.
mysql> SELECT YEARWEEK('1987-01-01');
-> 198652
The week number is different from what the
WEEK()
function would return
(0
) for optional arguments
0
or 1
, as
WEEK()
then returns the week in
the context of the given year.
Table 12.11 String Functions and Operators
Name | Description |
---|---|
ASCII() |
Return numeric value of left-most character |
BIN() |
Return a string containing binary representation of a number |
BIT_LENGTH() |
Return length of argument in bits |
CHAR() |
Return the character for each integer passed |
CHAR_LENGTH() |
Return number of characters in argument |
CHARACTER_LENGTH() |
Synonym for CHAR_LENGTH() |
CONCAT() |
Return concatenated string |
CONCAT_WS() |
Return concatenate with separator |
ELT() |
Return string at index number |
EXPORT_SET() |
Return a string such that for every bit set in the value bits, you get an on string and for every unset bit, you get an off string |
FIELD() |
Index (position) of first argument in subsequent arguments |
FIND_IN_SET() |
Index (position) of first argument within second argument |
FORMAT() |
Return a number formatted to specified number of decimal places |
FROM_BASE64() |
Decode base64 encoded string and return result |
HEX() |
Hexadecimal representation of decimal or string value |
INSERT() |
Insert substring at specified position up to specified number of characters |
INSTR() |
Return the index of the first occurrence of substring |
LCASE() |
Synonym for LOWER() |
LEFT() |
Return the leftmost number of characters as specified |
LENGTH() |
Return the length of a string in bytes |
LIKE |
Simple pattern matching |
LOAD_FILE() |
Load the named file |
LOCATE() |
Return the position of the first occurrence of substring |
LOWER() |
Return the argument in lowercase |
LPAD() |
Return the string argument, left-padded with the specified string |
LTRIM() |
Remove leading spaces |
MAKE_SET() |
Return a set of comma-separated strings that have the corresponding bit in bits set |
MATCH |
Perform full-text search |
MID() |
Return a substring starting from the specified position |
NOT LIKE |
Negation of simple pattern matching |
NOT REGEXP |
Negation of REGEXP |
OCT() |
Return a string containing octal representation of a number |
OCTET_LENGTH() |
Synonym for LENGTH() |
ORD() |
Return character code for leftmost character of the argument |
POSITION() |
Synonym for LOCATE() |
QUOTE() |
Escape the argument for use in an SQL statement |
REGEXP |
Whether string matches regular expression |
REPEAT() |
Repeat a string the specified number of times |
REPLACE() |
Replace occurrences of a specified string |
REVERSE() |
Reverse the characters in a string |
RIGHT() |
Return the specified rightmost number of characters |
RLIKE |
Whether string matches regular expression |
RPAD() |
Append string the specified number of times |
RTRIM() |
Remove trailing spaces |
SOUNDEX() |
Return a soundex string |
SOUNDS LIKE |
Compare sounds |
SPACE() |
Return a string of the specified number of spaces |
STRCMP() |
Compare two strings |
SUBSTR() |
Return the substring as specified |
SUBSTRING() |
Return the substring as specified |
SUBSTRING_INDEX() |
Return a substring from a string before the specified number of occurrences of the delimiter |
TO_BASE64() |
Return the argument converted to a base-64 string |
TRIM() |
Remove leading and trailing spaces |
UCASE() |
Synonym for UPPER() |
UNHEX() |
Return a string containing hex representation of a number |
UPPER() |
Convert to uppercase |
WEIGHT_STRING() |
Return the weight string for a string |
String-valued functions return NULL
if the
length of the result would be greater than the value of the
max_allowed_packet
system
variable. See Section 5.1.1, “Configuring the Server”.
For functions that operate on string positions, the first position is numbered 1.
For functions that take length arguments, noninteger arguments are rounded to the nearest integer.
Returns the numeric value of the leftmost character of the
string str
. Returns
0
if str
is the
empty string. Returns NULL
if
str
is NULL
.
ASCII()
works for 8-bit
characters.
mysql>SELECT ASCII('2');
-> 50 mysql>SELECT ASCII(2);
-> 50 mysql>SELECT ASCII('dx');
-> 100
See also the ORD()
function.
Returns a string representation of the binary value of
N
, where
N
is a longlong
(BIGINT
) number. This is
equivalent to
CONV(
.
Returns N
,10,2)NULL
if
N
is NULL
.
mysql> SELECT BIN(12);
-> '1100'
Returns the length of the string
str
in bits.
mysql> SELECT BIT_LENGTH('text');
-> 32
CHAR(
N
,...
[USING charset_name
])
CHAR()
interprets each argument
N
as an integer and returns a
string consisting of the characters given by the code values
of those integers. NULL
values are skipped.
mysql>SELECT CHAR(77,121,83,81,'76');
-> 'MySQL' mysql>SELECT CHAR(77,77.3,'77.3');
-> 'MMM'
CHAR()
arguments larger than
255 are converted into multiple result bytes. For example,
CHAR(256)
is equivalent to
CHAR(1,0)
, and
CHAR(256*256)
is equivalent to
CHAR(1,0,0)
:
mysql>SELECT HEX(CHAR(1,0)), HEX(CHAR(256));
+----------------+----------------+ | HEX(CHAR(1,0)) | HEX(CHAR(256)) | +----------------+----------------+ | 0100 | 0100 | +----------------+----------------+ mysql>SELECT HEX(CHAR(1,0,0)), HEX(CHAR(256*256));
+------------------+--------------------+ | HEX(CHAR(1,0,0)) | HEX(CHAR(256*256)) | +------------------+--------------------+ | 010000 | 010000 | +------------------+--------------------+
By default, CHAR()
returns a
binary string. To produce a string in a given character set,
use the optional USING
clause:
mysql> SELECT CHARSET(CHAR(X'65')), CHARSET(CHAR(X'65' USING utf8));
+----------------------+---------------------------------+
| CHARSET(CHAR(X'65')) | CHARSET(CHAR(X'65' USING utf8)) |
+----------------------+---------------------------------+
| binary | utf8 |
+----------------------+---------------------------------+
If USING
is given and the result string is
illegal for the given character set, a warning is issued.
Also, if strict SQL mode is enabled, the result from
CHAR()
becomes
NULL
.
Returns the length of the string
str
, measured in characters. A
multibyte character counts as a single character. This means
that for a string containing five 2-byte characters,
LENGTH()
returns
10
, whereas
CHAR_LENGTH()
returns
5
.
CHARACTER_LENGTH()
is a synonym
for CHAR_LENGTH()
.
Returns the string that results from concatenating the arguments. May have one or more arguments. If all arguments are nonbinary strings, the result is a nonbinary string. If the arguments include any binary strings, the result is a binary string. A numeric argument is converted to its equivalent nonbinary string form.
CONCAT()
returns
NULL
if any argument is
NULL
.
mysql>SELECT CONCAT('My', 'S', 'QL');
-> 'MySQL' mysql>SELECT CONCAT('My', NULL, 'QL');
-> NULL mysql>SELECT CONCAT(14.3);
-> '14.3'
For quoted strings, concatenation can be performed by placing the strings next to each other:
mysql> SELECT 'My' 'S' 'QL';
-> 'MySQL'
CONCAT_WS(
separator
,str1
,str2
,...)
CONCAT_WS()
stands for
Concatenate With Separator and is a special form of
CONCAT()
. The first argument is
the separator for the rest of the arguments. The separator is
added between the strings to be concatenated. The separator
can be a string, as can the rest of the arguments. If the
separator is NULL
, the result is
NULL
.
mysql>SELECT CONCAT_WS(',','First name','Second name','Last Name');
-> 'First name,Second name,Last Name' mysql>SELECT CONCAT_WS(',','First name',NULL,'Last Name');
-> 'First name,Last Name'
CONCAT_WS()
does not skip empty
strings. However, it does skip any NULL
values after the separator argument.
ELT()
returns the
N
th element of the list of strings:
str1
if
N
= 1
,
str2
if
N
= 2
, and so
on. Returns NULL
if
N
is less than 1
or greater than the number of arguments.
ELT()
is the complement of
FIELD()
.
mysql>SELECT ELT(1, 'Aa', 'Bb', 'Cc', 'Dd');
-> 'Aa' mysql>SELECT ELT(4, 'Aa', 'Bb', 'Cc', 'Dd');
-> 'Dd'
EXPORT_SET(
bits
,on
,off
[,separator
[,number_of_bits
]])
Returns a string such that for every bit set in the value
bits
, you get an
on
string and for every bit not set
in the value, you get an off
string. Bits in bits
are examined
from right to left (from low-order to high-order bits).
Strings are added to the result from left to right, separated
by the separator
string (the
default being the comma character ,
). The
number of bits examined is given by
number_of_bits
, which has a default
of 64 if not specified.
number_of_bits
is silently clipped
to 64 if larger than 64. It is treated as an unsigned integer,
so a value of −1 is effectively the same as 64.
mysql>SELECT EXPORT_SET(5,'Y','N',',',4);
-> 'Y,N,Y,N' mysql>SELECT EXPORT_SET(6,'1','0',',',10);
-> '0,1,1,0,0,0,0,0,0,0'
Returns the index (position) of str
in the str1
,
str2
,
str3
, ...
list.
Returns 0
if str
is not found.
If all arguments to FIELD()
are
strings, all arguments are compared as strings. If all
arguments are numbers, they are compared as numbers.
Otherwise, the arguments are compared as double.
If str
is NULL
,
the return value is 0
because
NULL
fails equality comparison with any
value. FIELD()
is the
complement of ELT()
.
mysql>SELECT FIELD('Bb', 'Aa', 'Bb', 'Cc', 'Dd', 'Ff');
-> 2 mysql>SELECT FIELD('Gg', 'Aa', 'Bb', 'Cc', 'Dd', 'Ff');
-> 0
Returns a value in the range of 1 to
N
if the string
str
is in the string list
strlist
consisting of
N
substrings. A string list is a
string composed of substrings separated by
,
characters. If the first argument is a
constant string and the second is a column of type
SET
, the
FIND_IN_SET()
function is
optimized to use bit arithmetic. Returns 0
if str
is not in
strlist
or if
strlist
is the empty string.
Returns NULL
if either argument is
NULL
. This function does not work properly
if the first argument contains a comma (,
)
character.
mysql> SELECT FIND_IN_SET('b','a,b,c,d');
-> 2
Formats the number X
to a format
like '#,###,###.##'
, rounded to
D
decimal places, and returns the
result as a string. If D
is
0
, the result has no decimal point or
fractional part.
The optional third parameter enables a locale to be specified
to be used for the result number's decimal point, thousands
separator, and grouping between separators. Permissible locale
values are the same as the legal values for the
lc_time_names
system variable
(see Section 10.16, “MySQL Server Locale Support”). If no locale is
specified, the default is 'en_US'
.
mysql>SELECT FORMAT(12332.123456, 4);
-> '12,332.1235' mysql>SELECT FORMAT(12332.1,4);
-> '12,332.1000' mysql>SELECT FORMAT(12332.2,0);
-> '12,332' mysql>SELECT FORMAT(12332.2,2,'de_DE');
-> '12.332,20'
Takes a string encoded with the base-64 encoded rules used by
TO_BASE64()
and returns the
decoded result as a binary string. The result is
NULL
if the argument is
NULL
or not a valid base-64 string. See the
description of TO_BASE64()
for
details about the encoding and decoding rules.
mysql> SELECT TO_BASE64('abc'), FROM_BASE64(TO_BASE64('abc'));
-> 'JWJj', 'abc'
For a string argument str
,
HEX()
returns a hexadecimal
string representation of str
where
each byte of each character in str
is converted to two hexadecimal digits. (Multibyte characters
therefore become more than two digits.) The inverse of this
operation is performed by the
UNHEX()
function.
For a numeric argument N
,
HEX()
returns a hexadecimal
string representation of the value of
N
treated as a longlong
(BIGINT
) number. This is
equivalent to
CONV(
.
The inverse of this operation is performed by
N
,10,16)CONV(HEX(
.
N
),16,10)
mysql>SELECT X'616263', HEX('abc'), UNHEX(HEX('abc'));
-> 'abc', 616263, 'abc' mysql>SELECT HEX(255), CONV(HEX(255),16,10);
-> 'FF', 255
Returns the string str
, with the
substring beginning at position pos
and len
characters long replaced by
the string newstr
. Returns the
original string if pos
is not
within the length of the string. Replaces the rest of the
string from position pos
if
len
is not within the length of the
rest of the string. Returns NULL
if any
argument is NULL
.
mysql>SELECT INSERT('Quadratic', 3, 4, 'What');
-> 'QuWhattic' mysql>SELECT INSERT('Quadratic', -1, 4, 'What');
-> 'Quadratic' mysql>SELECT INSERT('Quadratic', 3, 100, 'What');
-> 'QuWhat'
This function is multibyte safe.
Returns the position of the first occurrence of substring
substr
in string
str
. This is the same as the
two-argument form of LOCATE()
,
except that the order of the arguments is reversed.
mysql>SELECT INSTR('foobarbar', 'bar');
-> 4 mysql>SELECT INSTR('xbar', 'foobar');
-> 0
This function is multibyte safe, and is case-sensitive only if at least one argument is a binary string.
LCASE()
is a synonym for
LOWER()
.
In MySQL 5.7, LCASE()
used in
a view is rewritten as LOWER()
when storing
the view's definition. (Bug #12844279)
Returns the leftmost len
characters
from the string str
, or
NULL
if any argument is
NULL
.
mysql> SELECT LEFT('foobarbar', 5);
-> 'fooba'
This function is multibyte safe.
Returns the length of the string
str
, measured in bytes. A multibyte
character counts as multiple bytes. This means that for a
string containing five 2-byte characters,
LENGTH()
returns
10
, whereas
CHAR_LENGTH()
returns
5
.
mysql> SELECT LENGTH('text');
-> 4
The Length()
OpenGIS spatial function is
named ST_Length()
in MySQL.
Reads the file and returns the file contents as a string. To
use this function, the file must be located on the server
host, you must specify the full path name to the file, and you
must have the FILE
privilege.
The file must be readable by all and its size less than
max_allowed_packet
bytes. If
the secure_file_priv
system
variable is set to a nonempty directory name, the file to be
loaded must be located in that directory.
If the file does not exist or cannot be read because one of
the preceding conditions is not satisfied, the function
returns NULL
.
The character_set_filesystem
system variable controls interpretation of file names that are
given as literal strings.
mysql>UPDATE t
SET blob_col=LOAD_FILE('/tmp/picture')
WHERE id=1;
LOCATE(
,
substr
,str
)LOCATE(
substr
,str
,pos
)
The first syntax returns the position of the first occurrence
of substring substr
in string
str
. The second syntax returns the
position of the first occurrence of substring
substr
in string
str
, starting at position
pos
. Returns 0
if substr
is not in
str
. Returns
NULL
if substr
or str
is NULL
.
mysql>SELECT LOCATE('bar', 'foobarbar');
-> 4 mysql>SELECT LOCATE('xbar', 'foobar');
-> 0 mysql>SELECT LOCATE('bar', 'foobarbar', 5);
-> 7
This function is multibyte safe, and is case-sensitive only if at least one argument is a binary string.
Returns the string str
with all
characters changed to lowercase according to the current
character set mapping. The default is
latin1
(cp1252 West European).
mysql> SELECT LOWER('QUADRATICALLY');
-> 'quadratically'
LOWER()
(and
UPPER()
) are ineffective when
applied to binary strings
(BINARY
,
VARBINARY
,
BLOB
). To perform lettercase
conversion of a binary string, first convert it to a nonbinary
string using a character set appropriate for the data stored
in the string:
mysql>SET @str = BINARY 'New York';
mysql>SELECT LOWER(@str), LOWER(CONVERT(@str USING latin1));
+-------------+-----------------------------------+ | LOWER(@str) | LOWER(CONVERT(@str USING latin1)) | +-------------+-----------------------------------+ | New York | new york | +-------------+-----------------------------------+
For collations of Unicode character sets,
LOWER()
and
UPPER()
work according to the
Unicode Collation Algorithm (UCA) version in the collation
name, if there is one, and UCA 4.0.0 if no version is
specified. For example, utf8_unicode_520_ci
works according to UCA 5.2.0, whereas
utf8_unicode_ci
works according to UCA
4.0.0. See Section 10.10.1, “Unicode Character Sets”.
This function is multibyte safe.
In previous versions of MySQL, LOWER()
used
within a view was rewritten as
LCASE()
when storing the
view's definition. In MySQL 5.7,
LOWER()
is never rewritten in such cases,
but LCASE()
used within views is instead
rewritten as LOWER()
. (Bug #12844279)
Returns the string str
, left-padded
with the string padstr
to a length
of len
characters. If
str
is longer than
len
, the return value is shortened
to len
characters.
mysql>SELECT LPAD('hi',4,'??');
-> '??hi' mysql>SELECT LPAD('hi',1,'??');
-> 'h'
Returns the string str
with leading
space characters removed.
mysql> SELECT LTRIM(' barbar');
-> 'barbar'
This function is multibyte safe.
Returns a set value (a string containing substrings separated
by ,
characters) consisting of the strings
that have the corresponding bit in
bits
set.
str1
corresponds to bit 0,
str2
to bit 1, and so on.
NULL
values in
str1
,
str2
, ...
are
not appended to the result.
mysql>SELECT MAKE_SET(1,'a','b','c');
-> 'a' mysql>SELECT MAKE_SET(1 | 4,'hello','nice','world');
-> 'hello,world' mysql>SELECT MAKE_SET(1 | 4,'hello','nice',NULL,'world');
-> 'hello' mysql>SELECT MAKE_SET(0,'a','b','c');
-> ''
MID(
is a synonym for
str
,pos
,len
)SUBSTRING(
.
str
,pos
,len
)
Returns a string representation of the octal value of
N
, where
N
is a longlong
(BIGINT
) number. This is
equivalent to
CONV(
.
Returns N
,10,8)NULL
if
N
is NULL
.
mysql> SELECT OCT(12);
-> '14'
OCTET_LENGTH()
is a synonym for
LENGTH()
.
If the leftmost character of the string
str
is a multibyte character,
returns the code for that character, calculated from the
numeric values of its constituent bytes using this formula:
(1st byte code) + (2nd byte code * 256) + (3rd byte code * 256^2) ...
If the leftmost character is not a multibyte character,
ORD()
returns the same value as
the ASCII()
function.
mysql> SELECT ORD('2');
-> 50
POSITION(
is a synonym for
substr
IN str
)LOCATE(
.
substr
,str
)
Quotes a string to produce a result that can be used as a
properly escaped data value in an SQL statement. The string is
returned enclosed by single quotation marks and with each
instance of backslash (\
), single quote
('
), ASCII NUL
, and
Control+Z preceded by a backslash. If the argument is
NULL
, the return value is the word
“NULL” without enclosing single quotation marks.
mysql>SELECT QUOTE('Don\'t!');
-> 'Don\'t!' mysql>SELECT QUOTE(NULL);
-> NULL
For comparison, see the quoting rules for literal strings and within the C API in Section 9.1.1, “String Literals”, and Section 27.7.6.56, “mysql_real_escape_string_quote()”.
Returns a string consisting of the string
str
repeated
count
times. If
count
is less than 1, returns an
empty string. Returns NULL
if
str
or
count
are NULL
.
mysql> SELECT REPEAT('MySQL', 3);
-> 'MySQLMySQLMySQL'
Returns the string str
with all
occurrences of the string from_str
replaced by the string to_str
.
REPLACE()
performs a
case-sensitive match when searching for
from_str
.
mysql> SELECT REPLACE('www.mysql.com', 'w', 'Ww');
-> 'WwWwWw.mysql.com'
This function is multibyte safe.
Returns the string str
with the
order of the characters reversed.
mysql> SELECT REVERSE('abc');
-> 'cba'
This function is multibyte safe.
Returns the rightmost len
characters from the string str
, or
NULL
if any argument is
NULL
.
mysql> SELECT RIGHT('foobarbar', 4);
-> 'rbar'
This function is multibyte safe.
Returns the string str
,
right-padded with the string padstr
to a length of len
characters. If
str
is longer than
len
, the return value is shortened
to len
characters.
mysql>SELECT RPAD('hi',5,'?');
-> 'hi???' mysql>SELECT RPAD('hi',1,'?');
-> 'h'
This function is multibyte safe.
Returns the string str
with
trailing space characters removed.
mysql> SELECT RTRIM('barbar ');
-> 'barbar'
This function is multibyte safe.
Returns a soundex string from str
.
Two strings that sound almost the same should have identical
soundex strings. A standard soundex string is four characters
long, but the SOUNDEX()
function returns an arbitrarily long string. You can use
SUBSTRING()
on the result to
get a standard soundex string. All nonalphabetic characters in
str
are ignored. All international
alphabetic characters outside the A-Z range are treated as
vowels.
When using SOUNDEX()
, you
should be aware of the following limitations:
This function, as currently implemented, is intended to work well with strings that are in the English language only. Strings in other languages may not produce reliable results.
This function is not guaranteed to provide consistent
results with strings that use multibyte character sets,
including utf-8
. See Bug #22638 for
more information.
mysql>SELECT SOUNDEX('Hello');
-> 'H400' mysql>SELECT SOUNDEX('Quadratically');
-> 'Q36324'
This function implements the original Soundex algorithm, not the more popular enhanced version (also described by D. Knuth). The difference is that original version discards vowels first and duplicates second, whereas the enhanced version discards duplicates first and vowels second.
This is the same as
SOUNDEX(
.
expr1
)
= SOUNDEX(expr2
)
Returns a string consisting of N
space characters.
mysql> SELECT SPACE(6);
-> ' '
SUBSTR(
,
str
,pos
)SUBSTR(
,
str
FROM pos
)SUBSTR(
,
str
,pos
,len
)SUBSTR(
str
FROM pos
FOR
len
)
SUBSTR()
is a synonym for
SUBSTRING()
.
SUBSTRING(
,
str
,pos
)SUBSTRING(
,
str
FROM pos
)SUBSTRING(
,
str
,pos
,len
)SUBSTRING(
str
FROM pos
FOR
len
)
The forms without a len
argument
return a substring from string str
starting at position pos
. The forms
with a len
argument return a
substring len
characters long from
string str
, starting at position
pos
. The forms that use
FROM
are standard SQL syntax. It is also
possible to use a negative value for
pos
. In this case, the beginning of
the substring is pos
characters
from the end of the string, rather than the beginning. A
negative value may be used for pos
in any of the forms of this function. A value of 0 for
pos
returns an empty string.
For all forms of SUBSTRING()
,
the position of the first character in the string from which
the substring is to be extracted is reckoned as
1
.
mysql>SELECT SUBSTRING('Quadratically',5);
-> 'ratically' mysql>SELECT SUBSTRING('foobarbar' FROM 4);
-> 'barbar' mysql>SELECT SUBSTRING('Quadratically',5,6);
-> 'ratica' mysql>SELECT SUBSTRING('Sakila', -3);
-> 'ila' mysql>SELECT SUBSTRING('Sakila', -5, 3);
-> 'aki' mysql>SELECT SUBSTRING('Sakila' FROM -4 FOR 2);
-> 'ki'
This function is multibyte safe.
If len
is less than 1, the result
is the empty string.
SUBSTRING_INDEX(
str
,delim
,count
)
Returns the substring from string
str
before
count
occurrences of the delimiter
delim
. If
count
is positive, everything to
the left of the final delimiter (counting from the left) is
returned. If count
is negative,
everything to the right of the final delimiter (counting from
the right) is returned.
SUBSTRING_INDEX()
performs a
case-sensitive match when searching for
delim
.
mysql>SELECT SUBSTRING_INDEX('www.mysql.com', '.', 2);
-> 'www.mysql' mysql>SELECT SUBSTRING_INDEX('www.mysql.com', '.', -2);
-> 'mysql.com'
This function is multibyte safe.
Converts the string argument to base-64 encoded form and
returns the result as a character string with the connection
character set and collation. If the argument is not a string,
it is converted to a string before conversion takes place. The
result is NULL
if the argument is
NULL
. Base-64 encoded strings can be
decoded using the FROM_BASE64()
function.
mysql> SELECT TO_BASE64('abc'), FROM_BASE64(TO_BASE64('abc'));
-> 'JWJj', 'abc'
Different base-64 encoding schemes exist. These are the
encoding and decoding rules used by
TO_BASE64()
and
FROM_BASE64()
:
The encoding for alphabet value 62 is
'+'
.
The encoding for alphabet value 63 is
'/'
.
Encoded output consists of groups of 4 printable
characters. Each 3 bytes of the input data are encoded
using 4 characters. If the last group is incomplete, it is
padded with '='
characters to a length
of 4.
A newline is added after each 76 characters of encoded output to divide long output into multiple lines.
Decoding recognizes and ignores newline, carriage return, tab, and space.
TRIM([{BOTH | LEADING | TRAILING}
[
,
remstr
] FROM]
str
)TRIM([
remstr
FROM] str
)
Returns the string str
with all
remstr
prefixes or suffixes
removed. If none of the specifiers BOTH
,
LEADING
, or TRAILING
is
given, BOTH
is assumed.
remstr
is optional and, if not
specified, spaces are removed.
mysql>SELECT TRIM(' bar ');
-> 'bar' mysql>SELECT TRIM(LEADING 'x' FROM 'xxxbarxxx');
-> 'barxxx' mysql>SELECT TRIM(BOTH 'x' FROM 'xxxbarxxx');
-> 'bar' mysql>SELECT TRIM(TRAILING 'xyz' FROM 'barxxyz');
-> 'barx'
This function is multibyte safe.
UCASE()
is a synonym for
UPPER()
.
In MySQL 5.7, UCASE()
used in
a view is rewritten as UPPER()
when storing
the view's definition. (Bug #12844279)
For a string argument str
,
UNHEX(
interprets each pair of characters in the argument as a
hexadecimal number and converts it to the byte represented by
the number. The return value is a binary string.
str
)
mysql>SELECT UNHEX('4D7953514C');
-> 'MySQL' mysql>SELECT X'4D7953514C';
-> 'MySQL' mysql>SELECT UNHEX(HEX('string'));
-> 'string' mysql>SELECT HEX(UNHEX('1267'));
-> '1267'
The characters in the argument string must be legal
hexadecimal digits: '0'
..
'9'
, 'A'
..
'F'
, 'a'
..
'f'
. If the argument contains any
nonhexadecimal digits, the result is NULL
:
mysql> SELECT UNHEX('GG');
+-------------+
| UNHEX('GG') |
+-------------+
| NULL |
+-------------+
A NULL
result can occur if the argument to
UNHEX()
is a
BINARY
column, because values
are padded with 0x00 bytes when stored but those bytes are not
stripped on retrieval. For example, '41'
is
stored into a CHAR(3)
column as
'41 '
and retrieved as
'41'
(with the trailing pad space
stripped), so UNHEX()
for the
column value returns 'A'
. By contrast
'41'
is stored into a
BINARY(3)
column as
'41\0'
and retrieved as
'41\0'
(with the trailing pad
0x00
byte not stripped).
'\0'
is not a legal hexadecimal digit, so
UNHEX()
for the column value
returns NULL
.
For a numeric argument N
, the
inverse of
HEX(
is not performed by N
)UNHEX()
.
Use
CONV(HEX(
instead. See the description of
N
),16,10)HEX()
.
Returns the string str
with all
characters changed to uppercase according to the current
character set mapping. The default is
latin1
(cp1252 West European).
mysql> SELECT UPPER('Hej');
-> 'HEJ'
See the description of LOWER()
for information that also applies to
UPPER()
. This included
information about how to perform lettercase conversion of
binary strings (BINARY
,
VARBINARY
,
BLOB
) for which these functions
are ineffective, and information about case folding for
Unicode character sets.
This function is multibyte safe.
In previous versions of MySQL, UPPER()
used
within a view was rewritten as
UCASE()
when storing the
view's definition. In MySQL 5.7,
UPPER()
is never rewritten in such cases,
but UCASE()
used within views is instead
rewritten as UPPER()
. (Bug #12844279)
WEIGHT_STRING(
str
[AS {CHAR|BINARY}(N
)] [LEVEL
levels
]
[flags
])
levels
:
N
[ASC|DESC|REVERSE] [,
N
[ASC|DESC|REVERSE]] ...
This function returns the weight string for the input string. The return value is a binary string that represents the comparison and sorting value of the string. It has these properties:
If
WEIGHT_STRING(
=
str1
)WEIGHT_STRING(
,
then str2
)
(str1
=
str2
str1
and
str2
are considered equal)
If
WEIGHT_STRING(
<
str1
)WEIGHT_STRING(
,
then str2
)
(str1
<
str2
str1
sorts before
str2
)
WEIGHT_STRING()
is a debugging
function intended for internal use. Its behavior can change
without notice between MySQL versions. It can be used for
testing and debugging of collations, especially if you are
adding a new collation. See
Section 10.14, “Adding a Collation to a Character Set”.
This list briefly summarizes the arguments. More details are given in the discussion following the list.
str
: The input string
expression.
AS
clause: Optional; cast the input
string to a given type and length.
LEVEL
clause: Optional; specify weight
levels for the return value.
flags
: Optional; unused.
The input string, str
, is a string
expression. If the input is a nonbinary (character) string
such as a CHAR
,
VARCHAR
, or
TEXT
value, the return value
contains the collation weights for the string. If the input is
a binary (byte) string such as a
BINARY
,
VARBINARY
, or
BLOB
value, the return value is
the same as the input (the weight for each byte in a binary
string is the byte value). If the input is
NULL
,
WEIGHT_STRING()
returns
NULL
.
Examples:
mysql>SET @s = _latin1 'AB' COLLATE latin1_swedish_ci;
mysql>SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s));
+------+---------+------------------------+ | @s | HEX(@s) | HEX(WEIGHT_STRING(@s)) | +------+---------+------------------------+ | AB | 4142 | 4142 | +------+---------+------------------------+
mysql>SET @s = _latin1 'ab' COLLATE latin1_swedish_ci;
mysql>SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s));
+------+---------+------------------------+ | @s | HEX(@s) | HEX(WEIGHT_STRING(@s)) | +------+---------+------------------------+ | ab | 6162 | 4142 | +------+---------+------------------------+
mysql>SET @s = CAST('AB' AS BINARY);
mysql>SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s));
+------+---------+------------------------+ | @s | HEX(@s) | HEX(WEIGHT_STRING(@s)) | +------+---------+------------------------+ | AB | 4142 | 4142 | +------+---------+------------------------+
mysql>SET @s = CAST('ab' AS BINARY);
mysql>SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s));
+------+---------+------------------------+ | @s | HEX(@s) | HEX(WEIGHT_STRING(@s)) | +------+---------+------------------------+ | ab | 6162 | 6162 | +------+---------+------------------------+
The preceding examples use
HEX()
to display the
WEIGHT_STRING()
result. Because
the result is a binary value,
HEX()
can be especially useful
when the result contains nonprinting values, to display it in
printable form:
mysql>SET @s = CONVERT(X'C39F' USING utf8) COLLATE utf8_czech_ci;
mysql>SELECT HEX(WEIGHT_STRING(@s));
+------------------------+ | HEX(WEIGHT_STRING(@s)) | +------------------------+ | 0FEA0FEA | +------------------------+
For non-NULL
return values, the data type
of the value is VARBINARY
if
its length is within the maximum length for
VARBINARY
, otherwise the data
type is BLOB
.
The AS
clause may be given to cast the
input string to a nonbinary or binary string and to force it
to a given length:
AS CHAR(
casts the string to a nonbinary string and pads it on the
right with spaces to a length of
N
)N
characters.
N
must be at least 1. If
N
is less than the length of
the input string, the string is truncated to
N
characters. No warning occurs
for truncation.
AS BINARY(
is similar but casts the string to a binary string,
N
)N
is measured in bytes (not
characters), and padding uses 0x00
bytes (not spaces).
mysql>SET NAMES 'latin1';
mysql>SELECT HEX(WEIGHT_STRING('ab' AS CHAR(4)));
+-------------------------------------+ | HEX(WEIGHT_STRING('ab' AS CHAR(4))) | +-------------------------------------+ | 41422020 | +-------------------------------------+ mysql>SET NAMES 'utf8';
mysql>SELECT HEX(WEIGHT_STRING('ab' AS CHAR(4)));
+-------------------------------------+ | HEX(WEIGHT_STRING('ab' AS CHAR(4))) | +-------------------------------------+ | 0041004200200020 | +-------------------------------------+
mysql> SELECT HEX(WEIGHT_STRING('ab' AS BINARY(4)));
+---------------------------------------+
| HEX(WEIGHT_STRING('ab' AS BINARY(4))) |
+---------------------------------------+
| 61620000 |
+---------------------------------------+
The LEVEL
clause may be given to specify
that the return value should contain weights for specific
collation levels.
The levels
specifier following the
LEVEL
keyword may be given either as a list
of one or more integers separated by commas, or as a range of
two integers separated by a dash. Whitespace around the
punctuation characters does not matter.
Examples:
LEVEL 1 LEVEL 2, 3, 5 LEVEL 1-3
Any level less than 1 is treated as 1. Any level greater than the maximum for the input string collation is treated as maximum for the collation. The maximum varies per collation, but is never greater than 6.
In a list of levels, levels must be given in increasing order. In a range of levels, if the second number is less than the first, it is treated as the first number (for example, 4-2 is the same as 4-4).
If the LEVEL
clause is omitted, MySQL
assumes LEVEL 1 -
, where
max
max
is the maximum level for the
collation.
If LEVEL
is specified using list syntax
(not range syntax), any level number can be followed by these
modifiers:
ASC
: Return the weights without
modification. This is the default.
DESC
: Return bitwise-inverted weights
(for example, 0x78f0 DESC
=
0x870f
).
REVERSE
: Return the weights in reverse
order (that is,the weights for the reversed string, with
the first character last and the last first).
Examples:
mysql> SELECT HEX(WEIGHT_STRING(0x007fff LEVEL 1));
+--------------------------------------+
| HEX(WEIGHT_STRING(0x007fff LEVEL 1)) |
+--------------------------------------+
| 007FFF |
+--------------------------------------+
mysql> SELECT HEX(WEIGHT_STRING(0x007fff LEVEL 1 DESC));
+-------------------------------------------+
| HEX(WEIGHT_STRING(0x007fff LEVEL 1 DESC)) |
+-------------------------------------------+
| FF8000 |
+-------------------------------------------+
mysql> SELECT HEX(WEIGHT_STRING(0x007fff LEVEL 1 REVERSE));
+----------------------------------------------+
| HEX(WEIGHT_STRING(0x007fff LEVEL 1 REVERSE)) |
+----------------------------------------------+
| FF7F00 |
+----------------------------------------------+
mysql> SELECT HEX(WEIGHT_STRING(0x007fff LEVEL 1 DESC REVERSE));
+---------------------------------------------------+
| HEX(WEIGHT_STRING(0x007fff LEVEL 1 DESC REVERSE)) |
+---------------------------------------------------+
| 0080FF |
+---------------------------------------------------+
The flags
clause currently is
unused.
If a string function is given a binary string as an argument, the resulting string is also a binary string. A number converted to a string is treated as a binary string. This affects only comparisons.
Normally, if any expression in a string comparison is case-sensitive, the comparison is performed in case-sensitive fashion.
expr
LIKE pat
[ESCAPE
'escape_char
']
Pattern matching using an SQL pattern. Returns
1
(TRUE
) or
0
(FALSE
). If either
expr
or
pat
is NULL
,
the result is NULL
.
The pattern need not be a literal string. For example, it can be specified as a string expression or table column.
Per the SQL standard, LIKE
performs matching on a per-character basis, thus it can
produce results different from the
=
comparison
operator:
mysql>SELECT 'ä' LIKE 'ae' COLLATE latin1_german2_ci;
+-----------------------------------------+ | 'ä' LIKE 'ae' COLLATE latin1_german2_ci | +-----------------------------------------+ | 0 | +-----------------------------------------+ mysql>SELECT 'ä' = 'ae' COLLATE latin1_german2_ci;
+--------------------------------------+ | 'ä' = 'ae' COLLATE latin1_german2_ci | +--------------------------------------+ | 1 | +--------------------------------------+
In particular, trailing spaces are significant, which is not
true for CHAR
or
VARCHAR
comparisons performed
with the =
operator:
mysql> SELECT 'a' = 'a ', 'a' LIKE 'a ';
+------------+---------------+
| 'a' = 'a ' | 'a' LIKE 'a ' |
+------------+---------------+
| 1 | 0 |
+------------+---------------+
1 row in set (0.00 sec)
With LIKE
you can use the
following two wildcard characters in the pattern:
%
matches any number of characters,
even zero characters.
_
matches exactly one character.
mysql>SELECT 'David!' LIKE 'David_';
-> 1 mysql>SELECT 'David!' LIKE '%D%v%';
-> 1
To test for literal instances of a wildcard character,
precede it by the escape character. If you do not specify
the ESCAPE
character,
\
is assumed.
\%
matches one %
character.
\_
matches one _
character.
mysql>SELECT 'David!' LIKE 'David\_';
-> 0 mysql>SELECT 'David_' LIKE 'David\_';
-> 1
To specify a different escape character, use the
ESCAPE
clause:
mysql> SELECT 'David_' LIKE 'David|_' ESCAPE '|';
-> 1
The escape sequence should be empty or one character long.
The expression must evaluate as a constant at execution
time. If the
NO_BACKSLASH_ESCAPES
SQL
mode is enabled, the sequence cannot be empty.
The following two statements illustrate that string comparisons are not case-sensitive unless one of the operands is case-sensitive (uses a case-sensitive collation or is a binary string):
mysql>SELECT 'abc' LIKE 'ABC';
-> 1 mysql>SELECT 'abc' LIKE _latin1 'ABC' COLLATE latin1_general_cs;
-> 0 mysql>SELECT 'abc' LIKE _latin1 'ABC' COLLATE latin1_bin;
-> 0 mysql>SELECT 'abc' LIKE BINARY 'ABC';
-> 0
As an extension to standard SQL, MySQL permits
LIKE
on numeric expressions.
mysql> SELECT 10 LIKE '1%';
-> 1
Because MySQL uses C escape syntax in strings (for
example, \n
to represent a newline
character), you must double any \
that
you use in LIKE
strings. For
example, to search for \n
, specify it
as \\n
. To search for
\
, specify it as
\\\\
; this is because the backslashes
are stripped once by the parser and again when the pattern
match is made, leaving a single backslash to be matched
against.
Exception: At the end of the pattern string, backslash can
be specified as \\
. At the end of the
string, backslash stands for itself because there is
nothing following to escape. Suppose that a table contains
the following values:
mysql> SELECT filename FROM t1;
+--------------+
| filename |
+--------------+
| C: |
| C:\ |
| C:\Programs |
| C:\Programs\ |
+--------------+
To test for values that end with backslash, you can match the values using either of the following patterns:
mysql>SELECT filename, filename LIKE '%\\' FROM t1;
+--------------+---------------------+ | filename | filename LIKE '%\\' | +--------------+---------------------+ | C: | 0 | | C:\ | 1 | | C:\Programs | 0 | | C:\Programs\ | 1 | +--------------+---------------------+ mysql>SELECT filename, filename LIKE '%\\\\' FROM t1;
+--------------+-----------------------+ | filename | filename LIKE '%\\\\' | +--------------+-----------------------+ | C: | 0 | | C:\ | 1 | | C:\Programs | 0 | | C:\Programs\ | 1 | +--------------+-----------------------+
expr
NOT LIKE pat
[ESCAPE
'escape_char
']
This is the same as NOT
(
.
expr
LIKE
pat
[ESCAPE
'escape_char
'])
Aggregate queries involving NOT
LIKE
comparisons with columns containing
NULL
may yield unexpected results. For
example, consider the following table and data:
CREATE TABLE foo (bar VARCHAR(10)); INSERT INTO foo VALUES (NULL), (NULL);
The query SELECT COUNT(*) FROM foo WHERE bar LIKE
'%baz%';
returns 0
. You might
assume that SELECT COUNT(*) FROM foo WHERE bar
NOT LIKE '%baz%';
would return
2
. However, this is not the case: The
second query returns 0
. This is because
NULL NOT LIKE
always returns
expr
NULL
, regardless of the value of
expr
. The same is true for
aggregate queries involving NULL
and
comparisons using
NOT
RLIKE
or NOT
REGEXP
. In such cases, you must test explicitly
for NOT NULL
using
OR
(and not
AND
), as shown here:
SELECT COUNT(*) FROM foo WHERE bar NOT LIKE '%baz%' OR bar IS NULL;
STRCMP()
returns
0
if the strings are the same,
-1
if the first argument is smaller than
the second according to the current sort order, and
1
otherwise.
mysql>SELECT STRCMP('text', 'text2');
-> -1 mysql>SELECT STRCMP('text2', 'text');
-> 1 mysql>SELECT STRCMP('text', 'text');
-> 0
STRCMP()
performs the
comparison using the collation of the arguments.
mysql>SET @s1 = _latin1 'x' COLLATE latin1_general_ci;
mysql>SET @s2 = _latin1 'X' COLLATE latin1_general_ci;
mysql>SET @s3 = _latin1 'x' COLLATE latin1_general_cs;
mysql>SET @s4 = _latin1 'X' COLLATE latin1_general_cs;
mysql>SELECT STRCMP(@s1, @s2), STRCMP(@s3, @s4);
+------------------+------------------+ | STRCMP(@s1, @s2) | STRCMP(@s3, @s4) | +------------------+------------------+ | 0 | 1 | +------------------+------------------+
If the collations are incompatible, one of the arguments must be converted to be compatible with the other. See Section 10.8.4, “Collation Coercibility in Expressions”.
mysql>SELECT STRCMP(@s1, @s3);
ERROR 1267 (HY000): Illegal mix of collations (latin1_general_ci,IMPLICIT) and (latin1_general_cs,IMPLICIT) for operation 'strcmp' mysql>SELECT STRCMP(@s1, @s3 COLLATE latin1_general_ci);
+--------------------------------------------+ | STRCMP(@s1, @s3 COLLATE latin1_general_ci) | +--------------------------------------------+ | 0 | +--------------------------------------------+
Table 12.13 Regular Expression Functions and Operators
Name | Description |
---|---|
NOT REGEXP |
Negation of REGEXP |
REGEXP |
Whether string matches regular expression |
RLIKE |
Whether string matches regular expression |
A regular expression is a powerful way of specifying a pattern for a complex search. This section discusses the operators available for regular expression matching and illustrates, with examples, some of the special characters and constructs that can be used for regular expression operations. See also Section 3.3.4.7, “Pattern Matching”.
MySQL uses Henry Spencer's implementation of regular
expressions, which is aimed at conformance with POSIX 1003.2.
MySQL uses the extended version to support regular expression
pattern-matching operations in SQL statements. This section does
not contain all the details that can be found in Henry Spencer's
regex(7)
manual page. That manual page is
included in MySQL source distributions, in the
regex.7
file under the
regex
directory.
,
expr
NOT REGEXP pat
expr
NOT RLIKE pat
This is the same as NOT
(
.
expr
REGEXP
pat
)
,
expr
REGEXP pat
expr
RLIKE pat
Returns 1 if the string expr
matches the regular expression specified by the pattern
pat
, 0 otherwise. If either
expr
or
pat
is NULL
,
the return value is NULL
.
RLIKE
is a
synonym for REGEXP
.
The pattern can be an extended regular expression, the syntax for which is discussed in Regular Expression Syntax. The pattern need not be a literal string. For example, it can be specified as a string expression or table column.
Because MySQL uses the C escape syntax in strings (for
example, \n
to represent the newline
character), you must double any \
that you use in your REGEXP
arguments.
Regular expression operations use the character set and collation of the string expression and pattern arguments when deciding the type of a character and performing the comparison. If the arguments have different character sets or collations, coercibility rules apply as described in Section 10.8.4, “Collation Coercibility in Expressions”. If either argument is a binary string, the arguments are handled in case-sensitive fashion as binary strings.
mysql>SELECT 'Michael!' REGEXP '.*';
+------------------------+ | 'Michael!' REGEXP '.*' | +------------------------+ | 1 | +------------------------+ mysql>SELECT 'new*\n*line' REGEXP 'new\\*.\\*line';
+---------------------------------------+ | 'new*\n*line' REGEXP 'new\\*.\\*line' | +---------------------------------------+ | 0 | +---------------------------------------+ mysql>SELECT 'a' REGEXP '^[a-d]';
+---------------------+ | 'a' REGEXP '^[a-d]' | +---------------------+ | 1 | +---------------------+ mysql>SELECT 'a' REGEXP 'A', 'a' REGEXP BINARY 'A';
+----------------+-----------------------+ | 'a' REGEXP 'A' | 'a' REGEXP BINARY 'A' | +----------------+-----------------------+ | 1 | 0 | +----------------+-----------------------+
The REGEXP
and
RLIKE
operators work in byte-wise fashion, so they are not
multibyte safe and may produce unexpected results with
multibyte character sets. In addition, these operators
compare characters by their byte values and accented
characters may not compare as equal even if a given
collation treats them as equal.
A regular expression describes a set of strings. The simplest
regular expression is one that has no special characters in
it. For example, the regular expression
hello
matches hello
and
nothing else.
Nontrivial regular expressions use certain special constructs
so that they can match more than one string. For example, the
regular expression hello|world
contains the
|
alternation operator and matches either
the hello
or world
.
As a more complex example, the regular expression
B[an]*s
matches any of the strings
Bananas
, Baaaaas
,
Bs
, and any other string starting with a
B
, ending with an s
, and
containing any number of a
or
n
characters in between.
A regular expression for the
REGEXP
operator may use any of
the following special characters and constructs:
^
Match the beginning of a string.
mysql>SELECT 'fo\nfo' REGEXP '^fo$';
-> 0 mysql>SELECT 'fofo' REGEXP '^fo';
-> 1
$
Match the end of a string.
mysql>SELECT 'fo\no' REGEXP '^fo\no$';
-> 1 mysql>SELECT 'fo\no' REGEXP '^fo$';
-> 0
.
Match any character (including carriage return and newline).
mysql>SELECT 'fofo' REGEXP '^f.*$';
-> 1 mysql>SELECT 'fo\r\nfo' REGEXP '^f.*$';
-> 1
a*
Match any sequence of zero or more a
characters.
mysql>SELECT 'Ban' REGEXP '^Ba*n';
-> 1 mysql>SELECT 'Baaan' REGEXP '^Ba*n';
-> 1 mysql>SELECT 'Bn' REGEXP '^Ba*n';
-> 1
a+
Match any sequence of one or more a
characters.
mysql>SELECT 'Ban' REGEXP '^Ba+n';
-> 1 mysql>SELECT 'Bn' REGEXP '^Ba+n';
-> 0
a?
Match either zero or one a
character.
mysql>SELECT 'Bn' REGEXP '^Ba?n';
-> 1 mysql>SELECT 'Ban' REGEXP '^Ba?n';
-> 1 mysql>SELECT 'Baan' REGEXP '^Ba?n';
-> 0
de|abc
Alternation; match either of the sequences
de
or abc
.
mysql>SELECT 'pi' REGEXP 'pi|apa';
-> 1 mysql>SELECT 'axe' REGEXP 'pi|apa';
-> 0 mysql>SELECT 'apa' REGEXP 'pi|apa';
-> 1 mysql>SELECT 'apa' REGEXP '^(pi|apa)$';
-> 1 mysql>SELECT 'pi' REGEXP '^(pi|apa)$';
-> 1 mysql>SELECT 'pix' REGEXP '^(pi|apa)$';
-> 0
(abc)*
Match zero or more instances of the sequence
abc
.
mysql>SELECT 'pi' REGEXP '^(pi)*$';
-> 1 mysql>SELECT 'pip' REGEXP '^(pi)*$';
-> 0 mysql>SELECT 'pipi' REGEXP '^(pi)*$';
-> 1
{1}
, {2,3}
Repetition;
{
and
n
}{
notation provide a more general way of writing regular
expressions that match many occurrences of the previous
atom (or “piece”) of the pattern.
m
,n
}m
and
n
are integers.
a*
Can be written as a{0,}
.
a+
Can be written as a{1,}
.
a?
Can be written as a{0,1}
.
To be more precise,
a{
matches
exactly n
}n
instances of
a
.
a{
matches n
,}n
or more instances of
a
.
a{
matches m
,n
}m
through
n
instances of
a
, inclusive. If both
m
and
n
are given,
m
must be less than or equal to
n
.
m
and
n
must be in the range from
0
to RE_DUP_MAX
(default 255), inclusive.
mysql>SELECT 'abcde' REGEXP 'a[bcd]{2}e';
-> 0 mysql>SELECT 'abcde' REGEXP 'a[bcd]{3}e';
-> 1 mysql>SELECT 'abcde' REGEXP 'a[bcd]{1,10}e';
-> 1
[a-dX]
, [^a-dX]
Matches any character that is (or is not, if
^
is used) either a
,
b
, c
,
d
or X
. A
-
character between two other
characters forms a range that matches all characters from
the first character to the second. For example,
[0-9]
matches any decimal digit. To
include a literal ]
character, it must
immediately follow the opening bracket
[
. To include a literal
-
character, it must be written first
or last. Any character that does not have a defined
special meaning inside a []
pair
matches only itself.
mysql>SELECT 'aXbc' REGEXP '[a-dXYZ]';
-> 1 mysql>SELECT 'aXbc' REGEXP '^[a-dXYZ]$';
-> 0 mysql>SELECT 'aXbc' REGEXP '^[a-dXYZ]+$';
-> 1 mysql>SELECT 'aXbc' REGEXP '^[^a-dXYZ]+$';
-> 0 mysql>SELECT 'gheis' REGEXP '^[^a-dXYZ]+$';
-> 1 mysql>SELECT 'gheisa' REGEXP '^[^a-dXYZ]+$';
-> 0
[.characters.]
Within a bracket expression (written using
[
and ]
), matches
the sequence of characters of that collating element.
characters
is either a single character
or a character name like newline
. The
following table lists the permissible character names.
The following table shows the permissible character names and the characters that they match. For characters given as numeric values, the values are represented in octal.
Name | Character | Name | Character |
---|---|---|---|
NUL |
0 |
SOH |
001 |
STX |
002 |
ETX |
003 |
EOT |
004 |
ENQ |
005 |
ACK |
006 |
BEL |
007 |
alert |
007 |
BS |
010 |
backspace |
'\b' |
HT |
011 |
tab |
'\t' |
LF |
012 |
newline |
'\n' |
VT |
013 |
vertical-tab |
'\v' |
FF |
014 |
form-feed |
'\f' |
CR |
015 |
carriage-return |
'\r' |
SO |
016 |
SI |
017 |
DLE |
020 |
DC1 |
021 |
DC2 |
022 |
DC3 |
023 |
DC4 |
024 |
NAK |
025 |
SYN |
026 |
ETB |
027 |
CAN |
030 |
EM |
031 |
SUB |
032 |
ESC |
033 |
IS4 |
034 |
FS |
034 |
IS3 |
035 |
GS |
035 |
IS2 |
036 |
RS |
036 |
IS1 |
037 |
US |
037 |
space |
' ' |
exclamation-mark |
'!' |
quotation-mark |
'"' |
number-sign |
'#' |
dollar-sign |
'$' |
percent-sign |
'%' |
ampersand |
'&' |
apostrophe |
'\'' |
left-parenthesis |
'(' |
right-parenthesis |
')' |
asterisk |
'*' |
plus-sign |
'+' |
comma |
',' |
hyphen |
'-' |
hyphen-minus |
'-' |
period |
'.' |
full-stop |
'.' |
slash |
'/' |
solidus |
'/' |
zero |
'0' |
one |
'1' |
two |
'2' |
three |
'3' |
four |
'4' |
five |
'5' |
six |
'6' |
seven |
'7' |
eight |
'8' |
nine |
'9' |
colon |
':' |
semicolon |
';' |
less-than-sign |
'<' |
equals-sign |
'=' |
greater-than-sign |
'>' |
question-mark |
'?' |
commercial-at |
'@' |
left-square-bracket |
'[' |
backslash |
'\\' |
reverse-solidus |
'\\' |
right-square-bracket |
']' |
circumflex |
'^' |
circumflex-accent |
'^' |
underscore |
'_' |
low-line |
'_' |
grave-accent |
'`' |
left-brace |
'{' |
left-curly-bracket |
'{' |
vertical-line |
'|' |
right-brace |
'}' |
right-curly-bracket |
'}' |
tilde |
'~' |
DEL |
177 |
mysql>SELECT '~' REGEXP '[[.~.]]';
-> 1 mysql>SELECT '~' REGEXP '[[.tilde.]]';
-> 1
[=character_class=]
Within a bracket expression (written using
[
and ]
),
[=character_class=]
represents an
equivalence class. It matches all characters with the same
collation value, including itself. For example, if
o
and (+)
are the
members of an equivalence class,
[[=o=]]
, [[=(+)=]]
,
and [o(+)]
are all synonymous. An
equivalence class may not be used as an endpoint of a
range.
[:character_class:]
Within a bracket expression (written using
[
and ]
),
[:character_class:]
represents a
character class that matches all characters belonging to
that class. The following table lists the standard class
names. These names stand for the character classes defined
in the ctype(3)
manual page. A
particular locale may provide other class names. A
character class may not be used as an endpoint of a range.
Character Class Name | Meaning |
---|---|
alnum |
Alphanumeric characters |
alpha |
Alphabetic characters |
blank |
Whitespace characters |
cntrl |
Control characters |
digit |
Digit characters |
graph |
Graphic characters |
lower |
Lowercase alphabetic characters |
print |
Graphic or space characters |
punct |
Punctuation characters |
space |
Space, tab, newline, and carriage return |
upper |
Uppercase alphabetic characters |
xdigit |
Hexadecimal digit characters |
mysql>SELECT 'justalnums' REGEXP '[[:alnum:]]+';
-> 1 mysql>SELECT '!!' REGEXP '[[:alnum:]]+';
-> 0
[[:<:]]
,
[[:>:]]
These markers stand for word boundaries. They match the
beginning and end of words, respectively. A word is a
sequence of word characters that is not preceded by or
followed by word characters. A word character is an
alphanumeric character in the alnum
class or an underscore (_
).
mysql>SELECT 'a word a' REGEXP '[[:<:]]word[[:>:]]';
-> 1 mysql>SELECT 'a xword a' REGEXP '[[:<:]]word[[:>:]]';
-> 0
To use a literal instance of a special character in a regular
expression, precede it by two backslash (\) characters. The
MySQL parser interprets one of the backslashes, and the
regular expression library interprets the other. For example,
to match the string 1+2
that contains the
special +
character, only the last of the
following regular expressions is the correct one:
mysql>SELECT '1+2' REGEXP '1+2';
-> 0 mysql>SELECT '1+2' REGEXP '1\+2';
-> 0 mysql>SELECT '1+2' REGEXP '1\\+2';
-> 1
MySQL has many operators and functions that return a string. This section answers the question: What is the character set and collation of such a string?
For simple functions that take string input and return a string
result as output, the output's character set and collation are
the same as those of the principal input value. For example,
UPPER(
returns a string with the same character string and collation as
X
)X
. The same applies for
INSTR()
,
LCASE()
,
LOWER()
,
LTRIM()
,
MID()
,
REPEAT()
,
REPLACE()
,
REVERSE()
,
RIGHT()
,
RPAD()
,
RTRIM()
,
SOUNDEX()
,
SUBSTRING()
,
TRIM()
,
UCASE()
, and
UPPER()
.
The REPLACE()
function, unlike
all other functions, always ignores the collation of the
string input and performs a case-sensitive comparison.
If a string input or function result is a binary string, the
string has the binary
character set and
collation. This can be checked by using the
CHARSET()
and
COLLATION()
functions, both of
which return binary
for a binary string
argument:
mysql> SELECT CHARSET(BINARY 'a'), COLLATION(BINARY 'a');
+---------------------+-----------------------+
| CHARSET(BINARY 'a') | COLLATION(BINARY 'a') |
+---------------------+-----------------------+
| binary | binary |
+---------------------+-----------------------+
For operations that combine multiple string inputs and return a single string output, the “aggregation rules” of standard SQL apply for determining the collation of the result:
If an explicit COLLATE
occurs, use
Y
Y
.
If explicit COLLATE
and Y
COLLATE
occur, raise an
error.
Z
Otherwise, if all collations are
Y
, use
Y
.
Otherwise, the result has no collation.
For example, with CASE ... WHEN a THEN b WHEN b THEN c
COLLATE
, the
resulting collation is X
ENDX
. The same
applies for UNION
,
||
,
CONCAT()
,
ELT()
,
GREATEST()
,
IF()
, and
LEAST()
.
For operations that convert to character data, the character set
and collation of the strings that result from the operations are
defined by the
character_set_connection
and
collation_connection
system
variables that determine the default connection character set
and collation (see Section 10.4, “Connection Character Sets and Collations”). This
applies only to CAST()
,
CONV()
,
FORMAT()
,
HEX()
, and
SPACE()
.
As of MySQL 5.7.19, an exception to the preceding priniciple
occurs for expressions for virtual generated columns. In such
expressions, the table character set is used for
CONV()
or
HEX()
results, regardless of
connection character set.
If there is any question about the character set or collation of
the result returned by a string function, use the
CHARSET()
or
COLLATION()
function to find out:
mysql>SELECT USER(), CHARSET(USER()), COLLATION(USER());
+----------------+-----------------+-------------------+ | USER() | CHARSET(USER()) | COLLATION(USER()) | +----------------+-----------------+-------------------+ | test@localhost | utf8 | utf8_general_ci | +----------------+-----------------+-------------------+ mysql>SELECT CHARSET(COMPRESS('abc')), COLLATION(COMPRESS('abc'));
+--------------------------+----------------------------+ | CHARSET(COMPRESS('abc')) | COLLATION(COMPRESS('abc')) | +--------------------------+----------------------------+ | binary | binary | +--------------------------+----------------------------+
MySQL uses what is known as a proleptic Gregorian calendar.
Every country that has switched from the Julian to the Gregorian calendar has had to discard at least ten days during the switch. To see how this works, consider the month of October 1582, when the first Julian-to-Gregorian switch occurred.
Monday | Tuesday | Wednesday | Thursday | Friday | Saturday | Sunday |
---|---|---|---|---|---|---|
1 | 2 | 3 | 4 | 15 | 16 | 17 |
18 | 19 | 20 | 21 | 22 | 23 | 24 |
25 | 26 | 27 | 28 | 29 | 30 | 31 |
There are no dates between October 4 and October 15. This discontinuity is called the cutover. Any dates before the cutover are Julian, and any dates following the cutover are Gregorian. Dates during a cutover are nonexistent.
A calendar applied to dates when it was not actually in use is
called proleptic. Thus, if
we assume there was never a cutover and Gregorian rules always
rule, we have a proleptic Gregorian calendar. This is what is used
by MySQL, as is required by standard SQL. For this reason, dates
prior to the cutover stored as MySQL
DATE
or
DATETIME
values must be adjusted to
compensate for the difference. It is important to realize that the
cutover did not occur at the same time in all countries, and that
the later it happened, the more days were lost. For example, in
Great Britain, it took place in 1752, when Wednesday September 2
was followed by Thursday September 14. Russia remained on the
Julian calendar until 1918, losing 13 days in the process, and
what is popularly referred to as its “October
Revolution” occurred in November according to the Gregorian
calendar.
MATCH
(
col1
,col2
,...)
AGAINST (expr
[search_modifier
])
search_modifier:
{
IN NATURAL LANGUAGE MODE
| IN NATURAL LANGUAGE MODE WITH QUERY EXPANSION
| IN BOOLEAN MODE
| WITH QUERY EXPANSION
}
MySQL has support for full-text indexing and searching:
A full-text index in MySQL is an index of type
FULLTEXT
.
Full-text indexes can be used only with
InnoDB
or
MyISAM
tables, and can be created
only for CHAR
,
VARCHAR
, or
TEXT
columns.
MySQL provides a built-in full-text ngram parser that supports Chinese, Japanese, and Korean (CJK), and an installable MeCab full-text parser plugin for Japanese. Parsing differences are outlined in Section 12.9.8, “ngram Full-Text Parser”, and Section 12.9.9, “MeCab Full-Text Parser Plugin”.
A FULLTEXT
index definition can be given in
the CREATE TABLE
statement when
a table is created, or added later using
ALTER TABLE
or
CREATE INDEX
.
For large data sets, it is much faster to load your data into
a table that has no FULLTEXT
index and then
create the index after that, than to load data into a table
that has an existing FULLTEXT
index.
Full-text searching is performed using
MATCH() ... AGAINST
syntax.
MATCH()
takes a comma-separated
list that names the columns to be searched.
AGAINST
takes a string to search for, and an
optional modifier that indicates what type of search to perform.
The search string must be a string value that is constant during
query evaluation. This rules out, for example, a table column
because that can differ for each row.
There are three types of full-text searches:
A natural language search interprets the search string as a phrase in natural human language (a phrase in free text). There are no special operators, with the exception of double quote (") characters. The stopword list applies. For more information about stopword lists, see Section 12.9.4, “Full-Text Stopwords”.
Full-text searches are natural language searches if the
IN NATURAL LANGUAGE MODE
modifier is given
or if no modifier is given. For more information, see
Section 12.9.1, “Natural Language Full-Text Searches”.
A boolean search interprets the search string using the rules
of a special query language. The string contains the words to
search for. It can also contain operators that specify
requirements such that a word must be present or absent in
matching rows, or that it should be weighted higher or lower
than usual. Certain common words (stopwords) are omitted from
the search index and do not match if present in the search
string. The IN BOOLEAN MODE
modifier
specifies a boolean search. For more information, see
Section 12.9.2, “Boolean Full-Text Searches”.
A query expansion search is a modification of a natural
language search. The search string is used to perform a
natural language search. Then words from the most relevant
rows returned by the search are added to the search string and
the search is done again. The query returns the rows from the
second search. The IN NATURAL LANGUAGE MODE WITH
QUERY EXPANSION
or WITH QUERY
EXPANSION
modifier specifies a query expansion
search. For more information, see
Section 12.9.3, “Full-Text Searches with Query Expansion”.
For information about FULLTEXT
query
performance, see Section 8.3.4, “Column Indexes”.
For more information about InnoDB
FULLTEXT
indexes, see
Section 14.6.2.4, “InnoDB FULLTEXT Indexes”.
Constraints on full-text searching are listed in Section 12.9.5, “Full-Text Restrictions”.
The myisam_ftdump utility dumps the contents of
a MyISAM
full-text index. This may be helpful
for debugging full-text queries. See
Section 4.6.2, “myisam_ftdump — Display Full-Text Index information”.
By default or with the IN NATURAL LANGUAGE
MODE
modifier, the
MATCH()
function performs a
natural language search for a string against a
text collection. A
collection is a set of one or more columns included in a
FULLTEXT
index. The search string is given as
the argument to AGAINST()
. For each row in
the table, MATCH()
returns a
relevance value; that is, a similarity measure between the
search string and the text in that row in the columns named in
the MATCH()
list.
mysql>CREATE TABLE articles (
id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY,
title VARCHAR(200),
body TEXT,
FULLTEXT (title,body)
) ENGINE=InnoDB;
Query OK, 0 rows affected (0.08 sec) mysql>INSERT INTO articles (title,body) VALUES
('MySQL Tutorial','DBMS stands for DataBase ...'),
('How To Use MySQL Well','After you went through a ...'),
('Optimizing MySQL','In this tutorial we will show ...'),
('1001 MySQL Tricks','1. Never run mysqld as root. 2. ...'),
('MySQL vs. YourSQL','In the following database comparison ...'),
('MySQL Security','When configured properly, MySQL ...');
Query OK, 6 rows affected (0.01 sec) Records: 6 Duplicates: 0 Warnings: 0 mysql>SELECT * FROM articles
WHERE MATCH (title,body)
AGAINST ('database' IN NATURAL LANGUAGE MODE);
+----+-------------------+------------------------------------------+ | id | title | body | +----+-------------------+------------------------------------------+ | 1 | MySQL Tutorial | DBMS stands for DataBase ... | | 5 | MySQL vs. YourSQL | In the following database comparison ... | +----+-------------------+------------------------------------------+ 2 rows in set (0.00 sec)
By default, the search is performed in case-insensitive fashion.
To perform a case-sensitive full-text search, use a binary
collation for the indexed columns. For example, a column that
uses the latin1
character set of can be
assigned a collation of latin1_bin
to make it
case-sensitive for full-text searches.
When MATCH()
is used in a
WHERE
clause, as in the example shown
earlier, the rows returned are automatically sorted with the
highest relevance first. Relevance values are nonnegative
floating-point numbers. Zero relevance means no similarity.
Relevance is computed based on the number of words in the row
(document), the number of unique words in the row, the total
number of words in the collection, and the number of rows that
contain a particular word.
The term “document” may be used interchangeably with the term “row”, and both terms refer to the indexed part of the row. The term “collection” refers to the indexed columns and encompasses all rows.
To simply count matches, you could use a query like this:
mysql>SELECT COUNT(*) FROM articles
WHERE MATCH (title,body)
AGAINST ('database' IN NATURAL LANGUAGE MODE);
+----------+ | COUNT(*) | +----------+ | 2 | +----------+ 1 row in set (0.00 sec)
You might find it quicker to rewrite the query as follows:
mysql>SELECT
COUNT(IF(MATCH (title,body) AGAINST ('database' IN NATURAL LANGUAGE MODE), 1, NULL))
AS count
FROM articles;
+-------+ | count | +-------+ | 2 | +-------+ 1 row in set (0.03 sec)
The first query does some extra work (sorting the results by
relevance) but also can use an index lookup based on the
WHERE
clause. The index lookup might make the
first query faster if the search matches few rows. The second
query performs a full table scan, which might be faster than the
index lookup if the search term was present in most rows.
For natural-language full-text searches, the columns named in
the MATCH()
function must be the
same columns included in some FULLTEXT
index
in your table. For the preceding query, note that the columns
named in the MATCH()
function
(title
and body
) are the
same as those named in the definition of the
article
table's FULLTEXT
index. To search the title
or
body
separately, you would create separate
FULLTEXT
indexes for each column.
You can also perform a boolean search or a search with query expansion. These search types are described in Section 12.9.2, “Boolean Full-Text Searches”, and Section 12.9.3, “Full-Text Searches with Query Expansion”.
A full-text search that uses an index can name columns only from
a single table in the MATCH()
clause because an index cannot span multiple tables. For
MyISAM
tables, a boolean search can be done
in the absence of an index (albeit more slowly), in which case
it is possible to name columns from multiple tables.
The preceding example is a basic illustration that shows how to
use the MATCH()
function where
rows are returned in order of decreasing relevance. The next
example shows how to retrieve the relevance values explicitly.
Returned rows are not ordered because the
SELECT
statement includes neither
WHERE
nor ORDER BY
clauses:
mysql>SELECT id, MATCH (title,body)
AGAINST ('Tutorial' IN NATURAL LANGUAGE MODE) AS score
FROM articles;
+----+---------------------+ | id | score | +----+---------------------+ | 1 | 0.22764469683170319 | | 2 | 0 | | 3 | 0.22764469683170319 | | 4 | 0 | | 5 | 0 | | 6 | 0 | +----+---------------------+ 6 rows in set (0.00 sec)
The following example is more complex. The query returns the
relevance values and it also sorts the rows in order of
decreasing relevance. To achieve this result, specify
MATCH()
twice: once in the
SELECT
list and once in the
WHERE
clause. This causes no additional
overhead, because the MySQL optimizer notices that the two
MATCH()
calls are identical and
invokes the full-text search code only once.
mysql>SELECT id, body, MATCH (title,body) AGAINST
('Security implications of running MySQL as root'
IN NATURAL LANGUAGE MODE) AS score
FROM articles WHERE MATCH (title,body) AGAINST
('Security implications of running MySQL as root'
IN NATURAL LANGUAGE MODE);
+----+-------------------------------------+-----------------+ | id | body | score | +----+-------------------------------------+-----------------+ | 4 | 1. Never run mysqld as root. 2. ... | 1.5219271183014 | | 6 | When configured properly, MySQL ... | 1.3114095926285 | +----+-------------------------------------+-----------------+ 2 rows in set (0.00 sec)
A phrase that is enclosed within double quote
("
) characters matches only rows that contain
the phrase literally, as it was typed. The
full-text engine splits the phrase into words and performs a
search in the FULLTEXT
index for the words.
Nonword characters need not be matched exactly: Phrase searching
requires only that matches contain exactly the same words as the
phrase and in the same order. For example, "test
phrase"
matches "test, phrase"
. If
the phrase contains no words that are in the index, the result
is empty. For example, if all words are either stopwords or
shorter than the minimum length of indexed words, the result is
empty.
The MySQL FULLTEXT
implementation regards any
sequence of true word characters (letters, digits, and
underscores) as a word. That sequence may also contain
apostrophes ('
), but not more than one in a
row. This means that aaa'bbb
is regarded as
one word, but aaa''bbb
is regarded as two
words. Apostrophes at the beginning or the end of a word are
stripped by the FULLTEXT
parser;
'aaa'bbb'
would be parsed as
aaa'bbb
.
The built-in FULLTEXT
parser determines where
words start and end by looking for certain delimiter characters;
for example,
(space),
,
(comma), and .
(period).
If words are not separated by delimiters (as in, for example,
Chinese), the built-in FULLTEXT
parser cannot
determine where a word begins or ends. To be able to add words
or other indexed terms in such languages to a
FULLTEXT
index that uses the built-in
FULLTEXT
parser, you must preprocess them so
that they are separated by some arbitrary delimiter.
Alternatively, you can create FULLTEXT
indexes using the ngram parser plugin (for Chinese, Japanese, or
Korean) or the MeCab parser plugin (for Japanese).
It is possible to write a plugin that replaces the built-in
full-text parser. For details, see Section 28.2, “The MySQL Plugin API”.
For example parser plugin source code, see the
plugin/fulltext
directory of a MySQL source
distribution.
Some words are ignored in full-text searches:
Any word that is too short is ignored. The default minimum
length of words that are found by full-text searches is
three characters for InnoDB
search
indexes, or four characters for MyISAM
.
You can control the cutoff by setting a configuration option
before creating the index:
innodb_ft_min_token_size
configuration option for InnoDB
search
indexes, or ft_min_word_len
for MyISAM
.
This behavior does not apply to
FULLTEXT
indexes that use the ngram
parser. For the ngram parser, token length is defined by
the ngram_token_size
option.
Words in the stopword list are ignored. A stopword is a word
such as “the” or “some” that is so
common that it is considered to have zero semantic value.
There is a built-in stopword list, but it can be overridden
by a user-defined list. The stopword lists and related
configuration options are different for
InnoDB
search indexes and
MyISAM
ones. Stopword processing is
controlled by the configuration options
innodb_ft_enable_stopword
,
innodb_ft_server_stopword_table
,
and
innodb_ft_user_stopword_table
for InnoDB
search indexes, and
ft_stopword_file
for
MyISAM
ones.
See Section 12.9.4, “Full-Text Stopwords” to view default stopword lists and how to change them. The default minimum word length can be changed as described in Section 12.9.6, “Fine-Tuning MySQL Full-Text Search”.
Every correct word in the collection and in the query is weighted according to its significance in the collection or query. Thus, a word that is present in many documents has a lower weight, because it has lower semantic value in this particular collection. Conversely, if the word is rare, it receives a higher weight. The weights of the words are combined to compute the relevance of the row. This technique works best with large collections.
For very small tables, word distribution does not adequately
reflect their semantic value, and this model may sometimes
produce bizarre results for search indexes on
MyISAM
tables. For example, although the
word “MySQL” is present in every row of the
articles
table shown earlier, a search for
the word in a MyISAM
search index produces
no results:
mysql>SELECT * FROM articles
WHERE MATCH (title,body)
AGAINST ('MySQL' IN NATURAL LANGUAGE MODE);
Empty set (0.00 sec)
The search result is empty because the word “MySQL” is present in at least 50% of the rows, and so is effectively treated as a stopword. This filtering technique is more suitable for large data sets, where you might not want the result set to return every second row from a 1GB table, than for small data sets where it might cause poor results for popular terms.
The 50% threshold can surprise you when you first try
full-text searching to see how it works, and makes
InnoDB
tables more suited to
experimentation with full-text searches. If you create a
MyISAM
table and insert only one or two
rows of text into it, every word in the text occurs in at
least 50% of the rows. As a result, no search returns any
results until the table contains more rows. Users who need to
bypass the 50% limitation can build search indexes on
InnoDB
tables, or use the boolean search
mode explained in Section 12.9.2, “Boolean Full-Text Searches”.
MySQL can perform boolean full-text searches using the
IN BOOLEAN MODE
modifier. With this modifier,
certain characters have special meaning at the beginning or end
of words in the search string. In the following query, the
+
and -
operators indicate
that a word must be present or absent, respectively, for a match
to occur. Thus, the query retrieves all the rows that contain
the word “MySQL” but that do
not contain the word
“YourSQL”:
mysql>SELECT * FROM articles WHERE MATCH (title,body)
AGAINST ('+MySQL -YourSQL' IN BOOLEAN MODE);
+----+-----------------------+-------------------------------------+ | id | title | body | +----+-----------------------+-------------------------------------+ | 1 | MySQL Tutorial | DBMS stands for DataBase ... | | 2 | How To Use MySQL Well | After you went through a ... | | 3 | Optimizing MySQL | In this tutorial we will show ... | | 4 | 1001 MySQL Tricks | 1. Never run mysqld as root. 2. ... | | 6 | MySQL Security | When configured properly, MySQL ... | +----+-----------------------+-------------------------------------+
In implementing this feature, MySQL uses what is sometimes referred to as implied Boolean logic, in which
+
stands for AND
-
stands for NOT
[no operator] implies
OR
Boolean full-text searches have these characteristics:
They do not automatically sort rows in order of decreasing relevance.
InnoDB
tables require a
FULLTEXT
index on all columns of the
MATCH()
expression to perform
boolean queries. Boolean queries against a
MyISAM
search index can work even without
a FULLTEXT
index, although a search
executed in this fashion would be quite slow.
The minimum and maximum word length full-text parameters
apply to FULLTEXT
indexes created using
the built-in FULLTEXT
parser and MeCab
parser plugin.
innodb_ft_min_token_size
and
innodb_ft_max_token_size
are used for InnoDB
search indexes.
ft_min_word_len
and
ft_max_word_len
are used
for MyISAM
search indexes.
Minimum and maximum word length full-text parameters do not
apply to FULLTEXT
indexes created using
the ngram parser. ngram token size is defined by the
ngram_token_size
option.
The stopword list applies, controlled by
innodb_ft_enable_stopword
,
innodb_ft_server_stopword_table
,
and
innodb_ft_user_stopword_table
for InnoDB
search indexes, and
ft_stopword_file
for
MyISAM
ones.
InnoDB
full-text search does not support
the use of multiple operators on a single search word, as in
this example: '++apple'
. Use of multiple
operators on a single search word returns a syntax error to
standard out. MyISAM full-text search will successfully
process the same search ignoring all operators except for
the operator immediately adjacent to the search word.
InnoDB
full-text search only supports
leading plus or minus signs. For example,
InnoDB
supports
'+apple'
but does not support
'apple+'
. Specifying a trailing plus or
minus sign causes InnoDB
to report a
syntax error.
InnoDB
full-text search does not support
the use of a leading plus sign with wildcard
('+*'
), a plus and minus sign combination
('+-'
), or leading a plus and minus sign
combination ('+-apple'
). These invalid
queries return a syntax error.
InnoDB
full-text search does not support
the use of the @
symbol in boolean
full-text searches. The @
symbol is
reserved for use by the @distance
proximity search operator.
They do not use the 50% threshold that applies to
MyISAM
search indexes.
The boolean full-text search capability supports the following operators:
+
A leading or trailing plus sign indicates that this word
must be present in each row that is
returned. InnoDB
only supports leading
plus signs.
-
A leading or trailing minus sign indicates that this word
must not be present in any of the rows
that are returned. InnoDB
only supports
leading minus signs.
Note: The -
operator acts only to exclude
rows that are otherwise matched by other search terms. Thus,
a boolean-mode search that contains only terms preceded by
-
returns an empty result. It does not
return “all rows except those containing any of the
excluded terms.”
(no operator)
By default (when neither +
nor
-
is specified), the word is optional,
but the rows that contain it are rated higher. This mimics
the behavior of MATCH() ...
AGAINST()
without the IN BOOLEAN
MODE
modifier.
@
distance
This operator works on InnoDB
tables
only. It tests whether two or more words all start within a
specified distance from each other, measured in words.
Specify the search words within a double-quoted string
immediately before the
@
operator, for example, distance
MATCH(col1) AGAINST('"word1
word2 word3" @8' IN BOOLEAN MODE)
> <
These two operators are used to change a word's contribution
to the relevance value that is assigned to a row. The
>
operator increases the contribution
and the <
operator decreases it. See
the example following this list.
( )
Parentheses group words into subexpressions. Parenthesized groups can be nested.
~
A leading tilde acts as a negation operator, causing the
word's contribution to the row's relevance to be negative.
This is useful for marking “noise” words. A row
containing such a word is rated lower than others, but is
not excluded altogether, as it would be with the
-
operator.
*
The asterisk serves as the truncation (or wildcard)
operator. Unlike the other operators, it is
appended to the word to be affected.
Words match if they begin with the word preceding the
*
operator.
If a word is specified with the truncation operator, it is
not stripped from a boolean query, even if it is too short
or a stopword. Whether a word is too short is determined
from the
innodb_ft_min_token_size
setting for InnoDB
tables, or
ft_min_word_len
for
MyISAM
tables. These options are not
applicable to FULLTEXT
indexes that use
the ngram parser.
The wildcarded word is considered as a prefix that must be
present at the start of one or more words. If the minimum
word length is 4, a search for
'+
could return fewer rows than a search for
word
+the*''+
,
because the second query ignores the too-short search term
word
+the'the
.
"
A phrase that is enclosed within double quote
("
) characters matches only rows that
contain the phrase literally, as it was
typed. The full-text engine splits the phrase
into words and performs a search in the
FULLTEXT
index for the words. Nonword
characters need not be matched exactly: Phrase searching
requires only that matches contain exactly the same words as
the phrase and in the same order. For example,
"test phrase"
matches "test,
phrase"
.
If the phrase contains no words that are in the index, the result is empty. The words might not be in the index because of a combination of factors: if they do not exist in the text, are stopwords, or are shorter than the minimum length of indexed words.
The following examples demonstrate some search strings that use boolean full-text operators:
'apple banana'
Find rows that contain at least one of the two words.
'+apple +juice'
Find rows that contain both words.
'+apple macintosh'
Find rows that contain the word “apple”, but rank rows higher if they also contain “macintosh”.
'+apple -macintosh'
Find rows that contain the word “apple” but not “macintosh”.
'+apple ~macintosh'
Find rows that contain the word “apple”, but if
the row also contains the word “macintosh”,
rate it lower than if row does not. This is
“softer” than a search for '+apple
-macintosh'
, for which the presence of
“macintosh” causes the row not to be returned
at all.
'+apple +(>turnover <strudel)'
Find rows that contain the words “apple” and “turnover”, or “apple” and “strudel” (in any order), but rank “apple turnover” higher than “apple strudel”.
'apple*'
Find rows that contain words such as “apple”, “apples”, “applesauce”, or “applet”.
'"some words"'
Find rows that contain the exact phrase “some
words” (for example, rows that contain “some
words of wisdom” but not “some noise
words”). Note that the "
characters that enclose the phrase are operator characters
that delimit the phrase. They are not the quotation marks
that enclose the search string itself.
InnoDB
full-text search is
modeled on the
Sphinx full-text
search engine, and the algorithms used are based on
BM25
and
TF-IDF
ranking algorithms. For these reasons, relevancy rankings for
InnoDB
boolean full-text search may differ
from MyISAM
relevancy rankings.
InnoDB
uses a variation of the “term
frequency-inverse document frequency”
(TF-IDF
) weighting system to rank a
document's relevance for a given full-text search query. The
TF-IDF
weighting is based on how frequently
a word appears in a document, offset by how frequently the
word appears in all documents in the collection. In other
words, the more frequently a word appears in a document, and
the less frequently the word appears in the document
collection, the higher the document is ranked.
The term frequency (TF
) value is the number
of times that a word appears in a document. The inverse
document frequency (IDF
) value of a word is
calculated using the following formula, where
total_records
is the number of records in
the collection, and matching_records
is the
number of records that the search term appears in.
${IDF} = log10( ${total_records} / ${matching_records} )
When a document contains a word multiple times, the IDF value is multiplied by the TF value:
${TF} * ${IDF}
Using the TF
and IDF
values, the relevancy ranking for a document is calculated
using this formula:
${rank} = ${TF} * ${IDF} * ${IDF}
The formula is demonstrated in the following examples.
This example demonstrates the relevancy ranking calculation for a single-word search.
mysql> CREATE TABLE articles ( id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY, title VARCHAR(200), body TEXT, FULLTEXT (title,body) ) ENGINE=InnoDB; Query OK, 0 rows affected (1.04 sec) mysql> INSERT INTO articles (title,body) VALUES ('MySQL Tutorial','This database tutorial ...'), ("How To Use MySQL",'After you went through a ...'), ('Optimizing Your Database','In this database tutorial ...'), ('MySQL vs. YourSQL','When comparing databases ...'), ('MySQL Security','When configured properly, MySQL ...'), ('Database, Database, Database','database database database'), ('1001 MySQL Tricks','1. Never run mysqld as root. 2. ...'), ('MySQL Full-Text Indexes', 'MySQL fulltext indexes use a ..'); Query OK, 8 rows affected (0.06 sec) Records: 8 Duplicates: 0 Warnings: 0 mysql> SELECT id, title, body, MATCH (title,body) AGAINST ('database' IN BOOLEAN MODE) AS score FROM articles ORDER BY score DESC; +----+------------------------------+-------------------------------------+---------------------+ | id | title | body | score | +----+------------------------------+-------------------------------------+---------------------+ | 6 | Database, Database, Database | database database database | 1.0886961221694946 | | 3 | Optimizing Your Database | In this database tutorial ... | 0.36289870738983154 | | 1 | MySQL Tutorial | This database tutorial ... | 0.18144935369491577 | | 2 | How To Use MySQL | After you went through a ... | 0 | | 4 | MySQL vs. YourSQL | When comparing databases ... | 0 | | 5 | MySQL Security | When configured properly, MySQL ... | 0 | | 7 | 1001 MySQL Tricks | 1. Never run mysqld as root. 2. ... | 0 | | 8 | MySQL Full-Text Indexes | MySQL fulltext indexes use a .. | 0 | +----+------------------------------+-------------------------------------+---------------------+ 8 rows in set (0.00 sec)
There are 8 records in total, with 3 that match the
“database” search term. The first record
(id 6
) contains the search term 6 times and
has a relevancy ranking of
1.0886961221694946
. This ranking value is
calculated using a TF
value of 6 (the
“database” search term appears 6 times in record
id 6
) and an IDF
value
of 0.42596873216370745, which is calculated as follows (where
8 is the total number of records and 3 is the number of
records that the search term appears in):
${IDF} = log10( 8 / 3 ) = 0.42596873216370745
The TF
and IDF
values
are then entered into the ranking formula:
${rank} = ${TF} * ${IDF} * ${IDF}
Performing the calculation in the MySQL command-line client returns a ranking value of 1.088696164686938.
mysql> SELECT 6*log10(8/3)*log10(8/3); +-------------------------+ | 6*log10(8/3)*log10(8/3) | +-------------------------+ | 1.088696164686938 | +-------------------------+ 1 row in set (0.00 sec)
You may notice a slight difference in the ranking values
returned by the SELECT ... MATCH ...
AGAINST
statement and the MySQL command-line
client (1.0886961221694946
versus
1.088696164686938
). The difference is due
to how the casts between integers and floats/doubles are
performed internally by InnoDB
(along
with related precision and rounding decisions), and how they
are performed elsewhere, such as in the MySQL command-line
client or other types of calculators.
This example demonstrates the relevancy ranking calculation
for a multiple-word full-text search based on the
articles
table and data used in the
previous example.
If you search on more than one word, the relevancy ranking value is a sum of the relevancy ranking value for each word, as shown in this formula:
${rank} = ${TF} * ${IDF} * ${IDF} + ${TF} * ${IDF} * ${IDF}
Performing a search on two terms ('mysql tutorial') returns the following results:
mysql> SELECT id, title, body, MATCH (title,body) AGAINST ('mysql tutorial' IN BOOLEAN MODE) AS score FROM articles ORDER BY score DESC; +----+------------------------------+-------------------------------------+----------------------+ | id | title | body | score | +----+------------------------------+-------------------------------------+----------------------+ | 1 | MySQL Tutorial | This database tutorial ... | 0.7405621409416199 | | 3 | Optimizing Your Database | In this database tutorial ... | 0.3624762296676636 | | 5 | MySQL Security | When configured properly, MySQL ... | 0.031219376251101494 | | 8 | MySQL Full-Text Indexes | MySQL fulltext indexes use a .. | 0.031219376251101494 | | 2 | How To Use MySQL | After you went through a ... | 0.015609688125550747 | | 4 | MySQL vs. YourSQL | When comparing databases ... | 0.015609688125550747 | | 7 | 1001 MySQL Tricks | 1. Never run mysqld as root. 2. ... | 0.015609688125550747 | | 6 | Database, Database, Database | database database database | 0 | +----+------------------------------+-------------------------------------+----------------------+ 8 rows in set (0.00 sec)
In the first record (id 8
), 'mysql' appears
once and 'tutorial' appears twice. There are six matching
records for 'mysql' and two matching records for 'tutorial'.
The MySQL command-line client returns the expected ranking
value when inserting these values into the ranking formula for
a multiple word search:
mysql> SELECT (1*log10(8/6)*log10(8/6)) + (2*log10(8/2)*log10(8/2)); +-------------------------------------------------------+ | (1*log10(8/6)*log10(8/6)) + (2*log10(8/2)*log10(8/2)) | +-------------------------------------------------------+ | 0.7405621541938003 | +-------------------------------------------------------+ 1 row in set (0.00 sec)
The slight difference in the ranking values returned by the
SELECT ... MATCH ... AGAINST
statement
and the MySQL command-line client is explained in the
preceding example.
Full-text search supports query expansion (and in particular, its variant “blind query expansion”). This is generally useful when a search phrase is too short, which often means that the user is relying on implied knowledge that the full-text search engine lacks. For example, a user searching for “database” may really mean that “MySQL”, “Oracle”, “DB2”, and “RDBMS” all are phrases that should match “databases” and should be returned, too. This is implied knowledge.
Blind query expansion (also known as automatic relevance
feedback) is enabled by adding WITH QUERY
EXPANSION
or IN NATURAL LANGUAGE MODE WITH
QUERY EXPANSION
following the search phrase. It works
by performing the search twice, where the search phrase for the
second search is the original search phrase concatenated with
the few most highly relevant documents from the first search.
Thus, if one of these documents contains the word
“databases” and the word “MySQL”, the
second search finds the documents that contain the word
“MySQL” even if they do not contain the word
“database”. The following example shows this
difference:
mysql>SELECT * FROM articles
WHERE MATCH (title,body)
AGAINST ('database' IN NATURAL LANGUAGE MODE);
+----+-------------------+------------------------------------------+ | id | title | body | +----+-------------------+------------------------------------------+ | 1 | MySQL Tutorial | DBMS stands for DataBase ... | | 5 | MySQL vs. YourSQL | In the following database comparison ... | +----+-------------------+------------------------------------------+ 2 rows in set (0.00 sec) mysql>SELECT * FROM articles
WHERE MATCH (title,body)
AGAINST ('database' WITH QUERY EXPANSION);
+----+-----------------------+------------------------------------------+ | id | title | body | +----+-----------------------+------------------------------------------+ | 5 | MySQL vs. YourSQL | In the following database comparison ... | | 1 | MySQL Tutorial | DBMS stands for DataBase ... | | 3 | Optimizing MySQL | In this tutorial we will show ... | | 6 | MySQL Security | When configured properly, MySQL ... | | 2 | How To Use MySQL Well | After you went through a ... | | 4 | 1001 MySQL Tricks | 1. Never run mysqld as root. 2. ... | +----+-----------------------+------------------------------------------+ 6 rows in set (0.00 sec)
Another example could be searching for books by Georges Simenon about Maigret, when a user is not sure how to spell “Maigret”. A search for “Megre and the reluctant witnesses” finds only “Maigret and the Reluctant Witnesses” without query expansion. A search with query expansion finds all books with the word “Maigret” on the second pass.
Because blind query expansion tends to increase noise significantly by returning nonrelevant documents, use it only when a search phrase is short.
The stopword list is loaded and searched for full-text queries
using the server character set and collation (the values of the
character_set_server
and
collation_server
system
variables). False hits or misses might occur for stopword
lookups if the stopword file or columns used for full-text
indexing or searches have a character set or collation different
from character_set_server
or
collation_server
.
Case sensitivity of stopword lookups depends on the server
collation. For example, lookups are case-insensitive if the
collation is latin1_swedish_ci
, whereas
lookups are case-sensitive if the collation is
latin1_general_cs
or
latin1_bin
.
InnoDB
has a relatively short list of
default stopwords, because documents from technical, literary,
and other sources often use short words as keywords or in
significant phrases. For example, you might search for
“to be or not to be” and expect to get a sensible
result, rather than having all those words ignored.
To see the default InnoDB
stopword list,
query the
INFORMATION_SCHEMA.INNODB_FT_DEFAULT_STOPWORD
table.
mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_FT_DEFAULT_STOPWORD; +-------+ | value | +-------+ | a | | about | | an | | are | | as | | at | | be | | by | | com | | de | | en | | for | | from | | how | | i | | in | | is | | it | | la | | of | | on | | or | | that | | the | | this | | to | | was | | what | | when | | where | | who | | will | | with | | und | | the | | www | +-------+ 36 rows in set (0.00 sec)
To define your own stopword list for all
InnoDB
tables, define a table with the same
structure as the
INNODB_FT_DEFAULT_STOPWORD
table,
populate it with stopwords, and set the value of the
innodb_ft_server_stopword_table
option to a value in the form
before creating the full-text index. The stopword table must
have a single db_name
/table_name
VARCHAR
column
named value
. The following example
demonstrates creating and configuring a new global stopword
table for InnoDB
.
-- Create a new stopword table mysql> CREATE TABLE my_stopwords(value VARCHAR(30)) ENGINE = INNODB; Query OK, 0 rows affected (0.01 sec) -- Insert stopwords (for simplicity, a single stopword is used in this example) mysql> INSERT INTO my_stopwords(value) VALUES ('Ishmael'); Query OK, 1 row affected (0.00 sec) -- Create the table mysql> CREATE TABLE opening_lines ( id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY, opening_line TEXT(500), author VARCHAR(200), title VARCHAR(200) ) ENGINE=InnoDB; Query OK, 0 rows affected (0.01 sec) -- Insert data into the table mysql> INSERT INTO opening_lines(opening_line,author,title) VALUES ('Call me Ishmael.','Herman Melville','Moby-Dick'), ('A screaming comes across the sky.','Thomas Pynchon','Gravity\'s Rainbow'), ('I am an invisible man.','Ralph Ellison','Invisible Man'), ('Where now? Who now? When now?','Samuel Beckett','The Unnamable'), ('It was love at first sight.','Joseph Heller','Catch-22'), ('All this happened, more or less.','Kurt Vonnegut','Slaughterhouse-Five'), ('Mrs. Dalloway said she would buy the flowers herself.','Virginia Woolf','Mrs. Dalloway'), ('It was a pleasure to burn.','Ray Bradbury','Fahrenheit 451'); Query OK, 8 rows affected (0.00 sec) Records: 8 Duplicates: 0 Warnings: 0 -- Set the innodb_ft_server_stopword_table option to the new stopword table mysql> SET GLOBAL innodb_ft_server_stopword_table = 'test/my_stopwords'; Query OK, 0 rows affected (0.00 sec) -- Create the full-text index (which rebuilds the table if no FTS_DOC_ID column is defined) mysql> CREATE FULLTEXT INDEX idx ON opening_lines(opening_line); Query OK, 0 rows affected, 1 warning (1.17 sec) Records: 0 Duplicates: 0 Warnings: 1
Verify that the specified stopword ('Ishmael') does not appear
by querying the words in
INFORMATION_SCHEMA.INNODB_FT_INDEX_TABLE
.
By default, words less than 3 characters in length or
greater than 84 characters in length do not appear in an
InnoDB
full-text search index. Maximum
and minimum word length values are configurable using the
innodb_ft_max_token_size
and
innodb_ft_min_token_size
variables. This default behavior does not apply to the ngram
parser plugin. ngram token size is defined by the
ngram_token_size
option.
mysql> SET GLOBAL innodb_ft_aux_table='test/opening_lines'; Query OK, 0 rows affected (0.00 sec) mysql> SELECT word FROM INFORMATION_SCHEMA.INNODB_FT_INDEX_TABLE LIMIT 15; +-----------+ | word | +-----------+ | across | | all | | burn | | buy | | call | | comes | | dalloway | | first | | flowers | | happened | | herself | | invisible | | less | | love | | man | +-----------+ 15 rows in set (0.00 sec)
To create stopword lists on a table-by-table basis, create
other stopword tables and use the
innodb_ft_user_stopword_table
option to specify the stopword table that you want to use
before you create the full-text index.
The stopword file is loaded and searched using
latin1
if
character_set_server
is
ucs2
, utf16
,
utf16le
, or utf32
.
To override the default stopword list for MyISAM tables, set
the ft_stopword_file
system
variable. (See Section 5.1.7, “Server System Variables”.) The
variable value should be the path name of the file containing
the stopword list, or the empty string to disable stopword
filtering. The server looks for the file in the data directory
unless an absolute path name is given to specify a different
directory. After changing the value of this variable or the
contents of the stopword file, restart the server and rebuild
your FULLTEXT
indexes.
The stopword list is free-form, separating stopwords with any
nonalphanumeric character such as newline, space, or comma.
Exceptions are the underscore character (_
)
and a single apostrophe ('
) which are
treated as part of a word. The character set of the stopword
list is the server's default character set; see
Section 10.3.2, “Server Character Set and Collation”.
The following list shows the default stopwords for
MyISAM
search indexes. In a MySQL source
distribution, you can find this list in the
storage/myisam/ft_static.c
file.
a's able about above according accordingly across actually after afterwards again against ain't all allow allows almost alone along already also although always am among amongst an and another any anybody anyhow anyone anything anyway anyways anywhere apart appear appreciate appropriate are aren't around as aside ask asking associated at available away awfully be became because become becomes becoming been before beforehand behind being believe below beside besides best better between beyond both brief but by c'mon c's came can can't cannot cant cause causes certain certainly changes clearly co com come comes concerning consequently consider considering contain containing contains corresponding could couldn't course currently definitely described despite did didn't different do does doesn't doing don't done down downwards during each edu eg eight either else elsewhere enough entirely especially et etc even ever every everybody everyone everything everywhere ex exactly example except far few fifth first five followed following follows for former formerly forth four from further furthermore get gets getting given gives go goes going gone got gotten greetings had hadn't happens hardly has hasn't have haven't having he he's hello help hence her here here's hereafter hereby herein hereupon hers herself hi him himself his hither hopefully how howbeit however i'd i'll i'm i've ie if ignored immediate in inasmuch inc indeed indicate indicated indicates inner insofar instead into inward is isn't it it'd it'll it's its itself just keep keeps kept know known knows last lately later latter latterly least less lest let let's like liked likely little look looking looks ltd mainly many may maybe me mean meanwhile merely might more moreover most mostly much must my myself name namely nd near nearly necessary need needs neither never nevertheless new next nine no nobody non none noone nor normally not nothing novel now nowhere obviously of off often oh ok okay old on once one ones only onto or other others otherwise ought our ours ourselves out outside over overall own particular particularly per perhaps placed please plus possible presumably probably provides que quite qv rather rd re really reasonably regarding regardless regards relatively respectively right said same saw say saying says second secondly see seeing seem seemed seeming seems seen self selves sensible sent serious seriously seven several shall she should shouldn't since six so some somebody somehow someone something sometime sometimes somewhat somewhere soon sorry specified specify specifying still sub such sup sure t's take taken tell tends th than thank thanks thanx that that's thats the their theirs them themselves then thence there there's thereafter thereby therefore therein theres thereupon these they they'd they'll they're they've think third this thorough thoroughly those though three through throughout thru thus to together too took toward towards tried tries truly try trying twice two un under unfortunately unless unlikely until unto up upon us use used useful uses using usually value various very via viz vs want wants was wasn't way we we'd we'll we're we've welcome well went were weren't what what's whatever when whence whenever where where's whereafter whereas whereby wherein whereupon wherever whether which while whither who who's whoever whole whom whose why will willing wish with within without won't wonder would wouldn't yes yet you you'd you'll you're you've your yours yourself yourselves zero
Full-text searches are supported for
InnoDB
and
MyISAM
tables only.
Full-text searches are not supported for partitioned tables. See Section 22.6, “Restrictions and Limitations on Partitioning”.
Full-text searches can be used with most multibyte character
sets. The exception is that for Unicode, the
utf8
character set can be used, but not
the ucs2
character set. Although
FULLTEXT
indexes on
ucs2
columns cannot be used, you can
perform IN BOOLEAN MODE
searches on a
ucs2
column that has no such index.
The remarks for utf8
also apply to
utf8mb4
, and the remarks for
ucs2
also apply to
utf16
, utf16le
, and
utf32
.
Ideographic languages such as Chinese and Japanese do not have word delimiters. Therefore, the built-in full-text parser cannot determine where words begin and end in these and other such languages.
A character-based ngram full-text parser that supports
Chinese, Japanese, and Korean (CJK), and a word-based MeCab
parser plugin that supports Japanese are provided for use
with InnoDB
and MySIAM
tables.
Although the use of multiple character sets within a single
table is supported, all columns in a
FULLTEXT
index must use the same
character set and collation.
The MATCH()
column list must
match exactly the column list in some
FULLTEXT
index definition for the table,
unless this MATCH()
is
IN BOOLEAN MODE
on a
MyISAM
table. For
MyISAM
tables, boolean-mode searches can
be done on nonindexed columns, although they are likely to
be slow.
The argument to AGAINST()
must be a
string value that is constant during query evaluation. This
rules out, for example, a table column because that can
differ for each row.
Index hints are more limited for FULLTEXT
searches than for non-FULLTEXT
searches.
See Section 8.9.4, “Index Hints”.
For InnoDB
, all DML operations
(INSERT
,
UPDATE
,
DELETE
) involving columns
with full-text indexes are processed at transaction commit
time. For example, for an INSERT
operation, an inserted string is tokenized and decomposed
into individual words. The individual words are then added
to full-text index tables when the transaction is committed.
As a result, full-text searches only return committed data.
The '%' character is not a supported wildcard character for full-text searches.
MySQL's full-text search capability has few user-tunable parameters. You can exert more control over full-text searching behavior if you have a MySQL source distribution because some changes require source code modifications. See Section 2.9, “Installing MySQL from Source”.
Full-text search is carefully tuned for effectiveness. Modifying the default behavior in most cases can actually decrease effectiveness. Do not alter the MySQL sources unless you know what you are doing.
Most full-text variables described in this section must be set at server startup time. A server restart is required to change them; they cannot be modified while the server is running.
Some variable changes require that you rebuild the
FULLTEXT
indexes in your tables. Instructions
for doing so are given later in this section.
The minimum and maximum lengths of words to be indexed are
defined by the
innodb_ft_min_token_size
and
innodb_ft_max_token_size
for
InnoDB
search indexes, and
ft_min_word_len
and
ft_max_word_len
for
MyISAM
ones.
Minimum and maximum word length full-text parameters do not
apply to FULLTEXT
indexes created using
the ngram parser. ngram token size is defined by the
ngram_token_size
option.
After changing any of these options, rebuild your
FULLTEXT
indexes for the change to take
effect. For example, to make two-character words searchable,
you could put the following lines in an option file:
[mysqld] innodb_ft_min_token_size=2 ft_min_word_len=2
Then restart the server and rebuild your
FULLTEXT
indexes. For
MyISAM
tables, note the remarks regarding
myisamchk in the instructions that follow
for rebuilding MyISAM
full-text indexes.
For MyISAM
search indexes, the 50%
threshold for natural language searches is determined by the
particular weighting scheme chosen. To disable it, look for
the following line in
storage/myisam/ftdefs.h
:
#define GWS_IN_USE GWS_PROB
Change that line to this:
#define GWS_IN_USE GWS_FREQ
Then recompile MySQL. There is no need to rebuild the indexes in this case.
By making this change, you severely
decrease MySQL's ability to provide adequate relevance
values for the MATCH()
function. If you really need to search for such common
words, it would be better to search using IN
BOOLEAN MODE
instead, which does not observe the
50% threshold.
To change the operators used for boolean full-text searches on
MyISAM
tables, set the
ft_boolean_syntax
system
variable. (InnoDB
does not have an
equivalent setting.) This variable can be changed while the
server is running, but you must have privileges sufficient to
set global system variables (see
Section 5.1.8.1, “System Variable Privileges”). No rebuilding
of indexes is necessary in this case.
For the built-in full-text parser, you can change the set of
characters that are considered word characters in several
ways, as described in the following list. After making the
modification, rebuild the indexes for each table that contains
any FULLTEXT
indexes. Suppose that you want
to treat the hyphen character ('-') as a word character. Use
one of these methods:
Modify the MySQL source: In
storage/innobase/handler/ha_innodb.cc
(for InnoDB
), or in
storage/myisam/ftdefs.h
(for
MyISAM
), see the
true_word_char()
and
misc_word_char()
macros. Add
'-'
to one of those macros and
recompile MySQL.
Modify a character set file: This requires no
recompilation. The true_word_char()
macro uses a “character type” table to
distinguish letters and numbers from other characters. .
You can edit the contents of the
<ctype><map>
array in one
of the character set XML files to specify that
'-'
is a “letter.” Then
use the given character set for your
FULLTEXT
indexes. For information about
the <ctype><map>
array
format, see Section 10.13.1, “Character Definition Arrays”.
Add a new collation for the character set used by the indexed columns, and alter the columns to use that collation. For general information about adding collations, see Section 10.14, “Adding a Collation to a Character Set”. For an example specific to full-text indexing, see Section 12.9.7, “Adding a Collation for Full-Text Indexing”.
For the changes to take effect, FULLTEXT
indexes must be rebuilt after modifying any of the following
full-text index variables:
innodb_ft_min_token_size
;
innodb_ft_max_token_size
;
innodb_ft_server_stopword_table
;
innodb_ft_user_stopword_table
;
innodb_ft_enable_stopword
;
ngram_token_size
. Modifying
innodb_ft_min_token_size
,
innodb_ft_max_token_size
, or
ngram_token_size
requires
restarting the server.
To rebuild FULLTEXT
indexes for an
InnoDB
table, use
ALTER TABLE
with the
DROP INDEX
and ADD INDEX
options to drop and re-create each index.
Running OPTIMIZE TABLE
on a
table with a full-text index rebuilds the full-text index,
removing deleted Document IDs and consolidating multiple
entries for the same word, where possible.
To optimize a full-text index, enable
innodb_optimize_fulltext_only
and run OPTIMIZE TABLE
.
mysql> set GLOBAL innodb_optimize_fulltext_only=ON; Query OK, 0 rows affected (0.01 sec) mysql> OPTIMIZE TABLE opening_lines; +--------------------+----------+----------+----------+ | Table | Op | Msg_type | Msg_text | +--------------------+----------+----------+----------+ | test.opening_lines | optimize | status | OK | +--------------------+----------+----------+----------+ 1 row in set (0.01 sec)
To avoid lengthy rebuild times for full-text indexes on large
tables, you can use the
innodb_ft_num_word_optimize
option to perform the optimization in stages. The
innodb_ft_num_word_optimize
option defines
the number of words that are optimized each time
OPTIMIZE TABLE
is run. The
default setting is 2000, which means that 2000 words are
optimized each time OPTIMIZE
TABLE
is run. Subsequent
OPTIMIZE TABLE
operations
continue from where the preceding
OPTIMIZE TABLE
operation ended.
If you modify full-text variables that affect indexing
(ft_min_word_len
,
ft_max_word_len
, or
ft_stopword_file
), or if you
change the stopword file itself, you must rebuild your
FULLTEXT
indexes after making the changes
and restarting the server.
To rebuild the FULLTEXT
indexes for a
MyISAM
table, it is sufficient to do a
QUICK
repair operation:
mysql> REPAIR TABLE tbl_name
QUICK;
Alternatively, use ALTER TABLE
as just described. In some cases, this may be faster than a
repair operation.
Each table that contains any FULLTEXT
index
must be repaired as just shown. Otherwise, queries for the
table may yield incorrect results, and modifications to the
table will cause the server to see the table as corrupt and in
need of repair.
If you use myisamchk to perform an
operation that modifies MyISAM
table
indexes (such as repair or analyze), the
FULLTEXT
indexes are rebuilt using the
default full-text parameter values for
minimum word length, maximum word length, and stopword file
unless you specify otherwise. This can result in queries
failing.
The problem occurs because these parameters are known only by
the server. They are not stored in MyISAM
index files. To avoid the problem if you have modified the
minimum or maximum word length or stopword file values used by
the server, specify the same
ft_min_word_len
,
ft_max_word_len
, and
ft_stopword_file
values for
myisamchk that you use for
mysqld. For example, if you have set the
minimum word length to 3, you can repair a table with
myisamchk like this:
myisamchk --recover --ft_min_word_len=3 tbl_name
.MYI
To ensure that myisamchk and the server use
the same values for full-text parameters, place each one in
both the [mysqld]
and
[myisamchk]
sections of an option file:
[mysqld] ft_min_word_len=3 [myisamchk] ft_min_word_len=3
An alternative to using myisamchk for
MyISAM
table index modification is to use
the REPAIR TABLE
,
ANALYZE TABLE
,
OPTIMIZE TABLE
, or
ALTER TABLE
statements. These
statements are performed by the server, which knows the proper
full-text parameter values to use.
This section describes how to add a new collation for full-text
searches using the built-in full-text parser. The sample
collation is like latin1_swedish_ci
but
treats the '-'
character as a letter rather
than as a punctuation character so that it can be indexed as a
word character. General information about adding collations is
given in Section 10.14, “Adding a Collation to a Character Set”; it is assumed that
you have read it and are familiar with the files involved.
To add a collation for full-text indexing, use the following procedure. The instructions here add a collation for a simple character set, which as discussed in Section 10.14, “Adding a Collation to a Character Set”, can be created using a configuration file that describes the character set properties. For a complex character set such as Unicode, create collations using C source files that describe the character set properties.
Add a collation to the Index.xml
file.
The collation ID must be unused, so choose a value different
from 1000 if that ID is already taken on your system.
<charset name="latin1"> ... <collation name="latin1_fulltext_ci" id="1000"/> </charset>
Declare the sort order for the collation in the
latin1.xml
file. In this case, the
order can be copied from
latin1_swedish_ci
:
<collation name="latin1_fulltext_ci"> <map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map> </collation>
Modify the ctype
array in
latin1.xml
. Change the value
corresponding to 0x2D (which is the code for the
'-'
character) from 10 (punctuation) to
01 (uppercase letter). In the following array, this is the
element in the fourth row down, third value from the end.
<ctype>
<map>
00
20 20 20 20 20 20 20 20 20 28 28 28 28 28 20 20
20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
48 10 10 10 10 10 10 10 10 10 10 10 10 01
10 10
84 84 84 84 84 84 84 84 84 84 10 10 10 10 10 10
10 81 81 81 81 81 81 01 01 01 01 01 01 01 01 01
01 01 01 01 01 01 01 01 01 01 01 10 10 10 10 10
10 82 82 82 82 82 82 02 02 02 02 02 02 02 02 02
02 02 02 02 02 02 02 02 02 02 02 10 10 10 10 20
10 00 10 02 10 10 10 10 10 10 01 10 01 00 01 00
00 10 10 10 10 10 10 10 10 10 02 10 02 00 02 01
48 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10
10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10
01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01
01 01 01 01 01 01 01 10 01 01 01 01 01 01 01 02
02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02
02 02 02 02 02 02 02 10 02 02 02 02 02 02 02 02
</map>
</ctype>
Restart the server.
To employ the new collation, include it in the definition of columns that are to use it:
mysql>DROP TABLE IF EXISTS t1;
Query OK, 0 rows affected (0.13 sec) mysql>CREATE TABLE t1 (
a TEXT CHARACTER SET latin1 COLLATE latin1_fulltext_ci,
FULLTEXT INDEX(a)
) ENGINE=InnoDB;
Query OK, 0 rows affected (0.47 sec)
Test the collation to verify that hyphen is considered as a word character:
mysql>INSERT INTO t1 VALUEs ('----'),('....'),('abcd');
Query OK, 3 rows affected (0.22 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql>SELECT * FROM t1 WHERE MATCH a AGAINST ('----' IN BOOLEAN MODE);
+------+ | a | +------+ | ---- | +------+ 1 row in set (0.00 sec)
The built-in MySQL full-text parser uses the white space between
words as a delimiter to determine where words begin and end,
which is a limitation when working with ideographic languages
that do not use word delimiters. To address this limitation,
MySQL provides an ngram full-text parser that supports Chinese,
Japanese, and Korean (CJK). The ngram full-text parser is
supported for use with InnoDB
and
MyISAM
.
MySQL also provides a MeCab full-text parser plugin for Japanese, which tokenizes documents into meaningful words. For more information, see Section 12.9.9, “MeCab Full-Text Parser Plugin”.
An ngram is a contiguous sequence of
n
characters from a given sequence of
text. The ngram parser tokenizes a sequence of text into a
contiguous sequence of n
characters.
For example, you can tokenize “abcd” for different
values of n
using the ngram full-text
parser.
n=1: 'a', 'b', 'c', 'd' n=2: 'ab', 'bc', 'cd' n=3: 'abc', 'bcd' n=4: 'abcd'
The ngram full-text parser is a built-in server plugin. As with other built-in server plugins, it is automatically loaded when the server is started.
The full-text search syntax described in
Section 12.9, “Full-Text Search Functions” applies to the ngram parser
plugin. Differences in parsing behavior are described in this
section. Full-text-related configuration options, except for
minimum and maximum word length options
(innodb_ft_min_token_size
,
innodb_ft_max_token_size
,
ft_min_word_len
,
ft_max_word_len
) are also
applicable.
The ngram parser has a default ngram token size of 2 (bigram). For example, with a token size of 2, the ngram parser parses the string “abc def” into four tokens: “ab”, “bc”, “de” and “ef”.
ngram token size is configurable using the
ngram_token_size
configuration
option, which has a minimum value of 1 and maximum value of 10.
Typically, ngram_token_size
is
set to the size of the largest token that you want to search
for. If you only intend to search for single characters, set
ngram_token_size
to 1. A
smaller token size produces a smaller full-text search index,
and faster searches. If you need to search for words comprised
of more than one character, set
ngram_token_size
accordingly.
For example, “Happy Birthday” is
“生日快乐” in
simplified Chinese, where
“生日” is
“birthday”, and
“快乐” translates
as “happy”. To search on two-character words such
as these, set ngram_token_size
to a value of 2 or higher.
As a read-only variable,
ngram_token_size
may only be
set as part of a startup string or in a configuration file:
Startup string:
mysqld --ngram_token_size=2
Configuration file:
[mysqld] ngram_token_size=2
The following minimum and maximum word length configuration
options are ignored for FULLTEXT
indexes
that use the ngram parser:
innodb_ft_min_token_size
,
innodb_ft_max_token_size
,
ft_min_word_len
, and
ft_max_word_len
.
To create a FULLTEXT
index that uses the
ngram parser, specify WITH PARSER ngram
with
CREATE TABLE
,
ALTER TABLE
, or
CREATE INDEX
.
The following example demonstrates creating a table with an
ngram
FULLTEXT
index,
inserting sample data (Simplified Chinese text), and viewing
tokenized data in the
INFORMATION_SCHEMA.INNODB_FT_INDEX_CACHE
table.
mysql> USE test; mysql> CREATE TABLE articles ( id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY, title VARCHAR(200), body TEXT, FULLTEXT (title,body) WITH PARSER ngram ) ENGINE=InnoDB CHARACTER SET utf8mb4; mysql> SET NAMES utf8mb4; INSERT INTO articles (title,body) VALUES ('数据库管理','在本教程中我将向你展示如何管理数据库'), ('数据库应用开发','学习开发数据库应用程序'); mysql> SET GLOBAL innodb_ft_aux_table="test/articles"; mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_FT_INDEX_CACHE ORDER BY doc_id, position;
To add a FULLTEXT
index to an existing table,
you can use ALTER TABLE
or
CREATE INDEX
. For example:
CREATE TABLE articles ( id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY, title VARCHAR(200), body TEXT ) ENGINE=InnoDB CHARACTER SET utf8; ALTER TABLE articles ADD FULLTEXT INDEX ft_index (title,body) WITH PARSER ngram; # Or: CREATE FULLTEXT INDEX ft_index ON articles (title,body) WITH PARSER ngram;
The ngram parser eliminates spaces when parsing. For example:
“ab cd” is parsed to “ab”, “cd”
“a bc” is parsed to “bc”
The built-in MySQL full-text parser compares words to entries in
the stopword list. If a word is equal to an entry in the
stopword list, the word is excluded from the index. For the
ngram parser, stopword handling is performed differently.
Instead of excluding tokens that are equal to entries in the
stopword list, the ngram parser excludes tokens that
contain stopwords. For example, assuming
ngram_token_size=2
, a document
that contains “a,b” is parsed to “a,”
and “,b”. If a comma (“,”) is defined
as a stopword, both “a,” and “,b” are
excluded from the index because they contain a comma.
By default, the ngram parser uses the default stopword list, which contains a list of English stopwords. For a stopword list applicable to Chinese, Japanese, or Korean, you must create your own. For information about creating a stopword list, see Section 12.9.4, “Full-Text Stopwords”.
Stopwords greater in length than
ngram_token_size
are ignored.
For natural language mode search, the
search term is converted to a union of ngram terms. For example,
the string “abc” (assuming
ngram_token_size=2
) is
converted to “ab bc”. Given two documents, one
containing “ab” and the other containing
“abc”, the search term “ab bc” matches
both documents.
For boolean mode search, the search term is
converted to an ngram phrase search. For example, the string
'abc' (assuming
ngram_token_size=2
) is
converted to '“ab bc”'. Given two documents, one
containing 'ab' and the other containing 'abc', the search
phrase '“ab bc”' only matches the document
containing 'abc'.
Because an ngram FULLTEXT
index contains only
ngrams, and does not contain information about the beginning of
terms, wildcard searches may return unexpected results. The
following behaviors apply to wildcard searches using ngram
FULLTEXT
search indexes:
If the prefix term of a wildcard search is shorter than
ngram token size, the query returns all indexed rows that
contain ngram tokens starting with the prefix term. For
example, assuming
ngram_token_size=2
, a
search on “a*” returns all rows starting with
“a”.
If the prefix term of a wildcard search is longer than ngram
token size, the prefix term is converted to an ngram phrase
and the wildcard operator is ignored. For example, assuming
ngram_token_size=2
, an
“abc*” wildcard search is converted to
“ab bc”.
Phrase searches are converted to ngram phrase searches. For example, The search phrase “abc” is converted to “ab bc”, which returns documents containing “abc” and “ab bc”.
The search phrase “abc def” is converted to “ab bc de ef”, which returns documents containing “abc def” and “ab bc de ef”. A document that contains “abcdef” is not returned.
The built-in MySQL full-text parser uses the white space between
words as a delimiter to determine where words begin and end,
which is a limitation when working with ideographic languages
that do not use word delimiters. To address this limitation for
Japanese, MySQL provides a MeCab full-text parser plugin. The
MeCab full-text parser plugin is supported for use with
InnoDB
and
MyISAM
.
MySQL also provides an ngram full-text parser plugin that supports Japanese. For more information, see Section 12.9.8, “ngram Full-Text Parser”.
The MeCab full-text parser plugin is a full-text parser plugin
for Japanese that tokenizes a sequence of text into meaningful
words. For example, MeCab tokenizes
“データベース管理”
(“Database Management”) into
“データベース”
(“Database”) and
“管理”
(“Management”). By comparison, the
ngram full-text
parser tokenizes text into a contiguous sequence of
n
characters, where
n
represents a number between 1 and
10.
In addition to tokenizing text into meaningful words, MeCab indexes are typically smaller than ngram indexes, and MeCab full-text searches are generally faster. One drawback is that it may take longer for the MeCab full-text parser to tokenize documents, compared to the ngram full-text parser.
The full-text search syntax described in Section 12.9, “Full-Text Search Functions” applies to the MeCab parser plugin. Differences in parsing behavior are described in this section. Full-text related configuration options are also applicable.
For additional information about the MeCab parser, refer to the MeCab: Yet Another Part-of-Speech and Morphological Analyzer project on Github.
The MeCab parser plugin requires mecab
and
mecab-ipadic
.
On supported Fedora, Debian and Ubuntu platforms (except Ubuntu
12.04 where the system mecab
version is too
old), MySQL dynamically links to the system
mecab
installation if it is installed to
the default location. On other supported Unix-like platforms,
libmecab.so
is statically linked in
libpluginmecab.so
, which is located in the
MySQL plugin directory. mecab-ipadic
is
included in MySQL binaries and is located in
.
MYSQL_HOME
\lib\mecab
You can install mecab
and
mecab-ipadic
using a native package
management utility (on Fedora, Debian, and Ubuntu), or you can
build mecab
and
mecab-ipadic
from source. For information
about installing mecab
and
mecab-ipadic
using a native package
management utility, see
Installing MeCab From a
Binary Distribution (Optional). If you want to build
mecab
and mecab-ipadic
from source, see
Building MeCab From
Source (Optional).
On Windows, libmecab.dll
is found in the
MySQL bin
directory.
mecab-ipadic
is located in
.
MYSQL_HOME
/lib/mecab
To install and configure the MeCab parser plugin, perform the following steps:
In the MySQL configuration file, set the
mecab_rc_file
configuration
option to the location of the mecabrc
configuration file, which is the configuration file for
MeCab. If you are using the MeCab package distributed with
MySQL, the mecabrc
file is located in
MYSQL_HOME/lib/mecab/etc/
.
[mysqld] loose-mecab-rc-file=MYSQL_HOME/lib/mecab/etc/mecabrc
The loose
prefix is an
option modifier. The
mecab_rc_file
option is not
recognized by MySQL until the MeCaB parser plugin is
installed but it must be set before attempting to install
the MeCaB parser plugin. The loose
prefix
allows you restart MySQL without encountering an error due
to an unrecognized variable.
If you use your own MeCab installation, or build MeCab from
source, the location of the mecabrc
configuration file may differ.
For information about the MySQL configuration file and its location, see Section 4.2.2.2, “Using Option Files”.
Also in the MySQL configuration file, set the minimum token
size to 1 or 2, which are the values recommended for use
with the MeCab parser. For InnoDB
tables,
minimum token size is defined by the
innodb_ft_min_token_size
configuration option, which has a default value of 3. For
MyISAM
tables, minimum token size is
defined by ft_min_word_len
,
which has a default value of 4.
[mysqld] innodb_ft_min_token_size=1
Modify the mecabrc
configuration file
to specify the dictionary you want to use. The
mecab-ipadic
package distributed with
MySQL binaries includes three dictionaries
(ipadic_euc-jp
,
ipadic_sjis
, and
ipadic_utf-8
). The
mecabrc
configuration file packaged
with MySQL contains and entry similar to the following:
dicdir = /path/to/mysql/lib/mecab/lib/mecab/dic/ipadic_euc-jp
To use the ipadic_utf-8
dictionary, for
example, modify the entry as follows:
dicdir=MYSQL_HOME
/lib/mecab/dic/ipadic_utf-8
If you are using your own MeCab installation or have built
MeCab from source, the default dicdir
entry in the mecabrc
file will differ,
as will the dictionaries and their location.
After the MeCab parser plugin is installed, you can use
the mecab_charset
status
variable to view the character set used with MeCab. The
three MeCab dictionaries provided with the MySQL binary
support the following character sets.
The ipadic_euc-jp
dictionary
supports the ujis
and
eucjpms
character sets.
The ipadic_sjis
dictionary supports
the sjis
and
cp932
character sets.
The ipadic_utf-8
dictionary
supports the utf8
and
utf8mb4
character sets.
mecab_charset
only
reports the first supported character set. For example,
the ipadic_utf-8
dictionary supports
both utf8
and
utf8mb4
.
mecab_charset
always
reports utf8
when this dictionary is in
use.
Restart MySQL.
Install the MeCab parser plugin:
The MeCab parser plugin is installed using
INSTALL PLUGIN
syntax. The
plugin name is mecab
, and the shared
library name is libpluginmecab.so
. For
additional information about installing plugins, see
Section 5.5.1, “Installing and Uninstalling Plugins”.
INSTALL PLUGIN mecab SONAME 'libpluginmecab.so';
Once installed, the MeCab parser plugin loads at every normal MySQL restart.
Verify that the MeCab parser plugin is loaded using the
SHOW PLUGINS
statement.
mysql> SHOW PLUGINS;
A mecab
plugin should appear in the list
of plugins.
To create a FULLTEXT
index that uses the
mecab parser, specify WITH PARSER ngram
with
CREATE TABLE
,
ALTER TABLE
, or
CREATE INDEX
.
This example demonstrates creating a table with a
mecab
FULLTEXT
index,
inserting sample data, and viewing tokenized data in the
INFORMATION_SCHEMA.INNODB_FT_INDEX_CACHE
table:
mysql> USE test; mysql> CREATE TABLE articles ( id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY, title VARCHAR(200), body TEXT, FULLTEXT (title,body) WITH PARSER mecab ) ENGINE=InnoDB CHARACTER SET utf8; mysql> SET NAMES utf8; mysql> INSERT INTO articles (title,body) VALUES ('データベース管理','このチュートリアルでは、私はどのようにデータベースを管理する方法を紹介します'), ('データベースアプリケーション開発','データベースアプリケーションを開発することを学ぶ'); mysql> SET GLOBAL innodb_ft_aux_table="test/articles"; mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_FT_INDEX_CACHE ORDER BY doc_id, position;
To add a FULLTEXT
index to an existing table,
you can use ALTER TABLE
or
CREATE INDEX
. For example:
CREATE TABLE articles ( id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY, title VARCHAR(200), body TEXT ) ENGINE=InnoDB CHARACTER SET utf8; ALTER TABLE articles ADD FULLTEXT INDEX ft_index (title,body) WITH PARSER mecab; # Or: CREATE FULLTEXT INDEX ft_index ON articles (title,body) WITH PARSER mecab;
The MeCab parser uses spaces as separators in query strings. For example, the MeCab parser tokenizes データベース管理 as データベース and 管理.
By default, the MeCab parser uses the default stopword list, which contains a short list of English stopwords. For a stopword list applicable to Japanese, you must create your own. For information about creating stopword lists, see Section 12.9.4, “Full-Text Stopwords”.
For natural language mode search, the search term is converted to a union of tokens. For example, データベース管理 is converted to データベース 管理.
SELECT COUNT(*) FROM articles WHERE MATCH(title,body) AGAINST('データベース管理' IN NATURAL LANGUAGE MODE);
For boolean mode search, the search term is converted to a search phrase. For example, データベース管理 is converted to データベース 管理.
SELECT COUNT(*) FROM articles WHERE MATCH(title,body) AGAINST('データベース管理' IN BOOLEAN MODE);
Wildcard search terms are not tokenized. A search on データベース管理* is performed on the prefix, データベース管理.
SELECT COUNT(*) FROM articles WHERE MATCH(title,body) AGAINST('データベース*' IN BOOLEAN MODE);
Phrases are tokenized. For example, データベース管理 is tokenized as データベース 管理.
SELECT COUNT(*) FROM articles WHERE MATCH(title,body) AGAINST('"データベース管理"' IN BOOLEAN MODE);
This section describes how to install mecab
and mecab-ipadic
from a binary distribution
using a native package management utility. For example, on
Fedora, you can use Yum to perform the installation:
yum mecab-devel
On Debian or Ubuntu, you can perform an APT installation:
apt-get install mecab apt-get install mecab-ipadic
If you want to build mecab
and
mecab-ipadic
from source, basic
installation steps are provided below. For additional
information, refer to the MeCab documentation.
Download the tar.gz packages for mecab
and mecab-ipadic
from
http://taku910.github.io/mecab/#download. As
of February, 2016, the latest available packages are
mecab-0.996.tar.gz
and
mecab-ipadic-2.7.0-20070801.tar.gz
.
Install mecab
:
tar zxfv mecab-0.996.tar cd mecab-0.996 ./configure make make check su make install
Install mecab-ipadic
:
tar zxfv mecab-ipadic-2.7.0-20070801.tar cd mecab-ipadic-2.7.0-20070801 ./configure make su make install
Compile MySQL using the
WITH_MECAB
CMake option. Set
the WITH_MECAB
option to
system
if you have installed
mecab
and
mecab-ipadic
to the default location.
-DWITH_MECAB=system
If you defined a custom installation directory, set
WITH_MECAB
to the custom
directory. For example:
-DWITH_MECAB=/path/to/mecab
Cast functions and operators enable conversion of values from one data type to another.
CONVERT()
with a
USING
clause converts data between different
character sets:
CONVERT(expr
USINGtranscoding_name
)
In MySQL, transcoding names are the same as the corresponding character set names.
Examples:
SELECT CONVERT('test' USING utf8); SELECT CONVERT(_latin1'Müller' USING utf8); INSERT INTO utf8_table (utf8_column) SELECT CONVERT(latin1_column USING utf8) FROM latin1_table;
To convert strings between different character sets, you can also
use CONVERT()
without
USING
, or
CAST()
:
CONVERT(string
, CHAR[(N
)] CHARACTER SETcharset_name
) CAST(string
AS CHAR[(N
)] CHARACTER SETcharset_name
)
Examples:
SELECT CONVERT('test', CHAR CHARACTER SET utf8); SELECT CAST('test' AS CHAR CHARACTER SET utf8);
If you specify CHARACTER SET
as just shown,
the character set and collation of the result are
charset_name
charset_name
and the default collation
of charset_name
. If you omit
CHARACTER SET
, the character
set and collation of the result are defined by the
charset_name
character_set_connection
and
collation_connection
system
variables that determine the default connection character set and
collation (see Section 10.4, “Connection Character Sets and Collations”).
A COLLATE
clause is not permitted within a
CONVERT()
or
CAST()
call, but you can apply it
to the function result. For example, these are legal:
SELECT CONVERT('test' USING utf8) COLLATE utf8_bin; SELECT CONVERT('test', CHAR CHARACTER SET utf8) COLLATE utf8_bin; SELECT CAST('test' AS CHAR CHARACTER SET utf8) COLLATE utf8_bin;
But these are illegal:
SELECT CONVERT('test' USING utf8 COLLATE utf8_bin); SELECT CONVERT('test', CHAR CHARACTER SET utf8 COLLATE utf8_bin); SELECT CAST('test' AS CHAR CHARACTER SET utf8 COLLATE utf8_bin);
Normally, you cannot compare a BLOB
value or other binary string in case-insensitive fashion because
binary strings use the binary
character set,
which has no collation with the concept of lettercase. To perform
a case-insensitive comparison, first use the
CONVERT()
or
CAST()
function to convert the
value to a nonbinary string. Comparisons of the resulting string
use its collation. For example, if the conversion result character
set has a case-insensitive collation, a
LIKE
operation is not case-sensitive.
That is true for the following operation because the default
latin1
collation
(latin1_swedish_ci
) is not case-sensitive:
SELECT 'A' LIKE CONVERT(blob_col
USING latin1) FROMtbl_name
;
To specify a particular collation for the converted string, use a
COLLATE
clause following the
CONVERT()
call:
SELECT 'A' LIKE CONVERT(blob_col
USING latin1) COLLATE latin1_german1_ci FROMtbl_name
;
To use a different character set, substitute its name for
latin1
in the preceding statements (and
similarly to use a different collation).
CONVERT()
and
CAST()
can be used more generally
for comparing strings represented in different character sets. For
example, a comparison of these strings results in an error because
they have different character sets:
mysql>SET @s1 = _latin1 'abc', @s2 = _latin2 'abc';
mysql>SELECT @s1 = @s2;
ERROR 1267 (HY000): Illegal mix of collations (latin1_swedish_ci,IMPLICIT) and (latin2_general_ci,IMPLICIT) for operation '='
Converting one of the strings to a character set compatible with the other enables the comparison to occur without error:
mysql> SELECT @s1 = CONVERT(@s2 USING latin1);
+---------------------------------+
| @s1 = CONVERT(@s2 USING latin1) |
+---------------------------------+
| 1 |
+---------------------------------+
For string literals, another way to specify the character set is
to use a character set introducer. _latin1
and
_latin2
in the preceding example are instances
of introducers. Unlike conversion functions such as
CAST()
, or
CONVERT()
, which convert a string
from one character set to another, an introducer designates a
string literal as having a particular character set, with no
conversion involved. For more information, see
Section 10.3.8, “Character Set Introducers”.
Character set conversion is also useful preceding lettercase
conversion of binary strings.
LOWER()
and
UPPER()
are ineffective when
applied directly to binary strings because the concept of
lettercase does not apply. To perform lettercase conversion of a
binary string, first convert it to a nonbinary string using a
character set appropriate for the data stored in the string:
mysql>SET @str = BINARY 'New York';
mysql>SELECT LOWER(@str), LOWER(CONVERT(@str USING latin1));
+-------------+-----------------------------------+ | LOWER(@str) | LOWER(CONVERT(@str USING latin1)) | +-------------+-----------------------------------+ | New York | new york | +-------------+-----------------------------------+
Be aware that if you convert an indexed column using
BINARY
,
CAST()
, or
CONVERT()
, MySQL may not be able to
use the index efficiently.
The cast functions are useful for creating a column with a
specific type in a
CREATE TABLE ...
SELECT
statement:
mysql>CREATE TABLE new_table SELECT CAST('2000-01-01' AS DATE) AS c1;
mysql>SHOW CREATE TABLE new_table\G
*************************** 1. row *************************** Table: new_table Create Table: CREATE TABLE `new_table` ( `c1` date DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=latin1
The cast functions are useful for sorting
ENUM
columns in lexical order.
Normally, sorting of ENUM
columns
occurs using the internal numeric values. Casting the values to
CHAR
results in a lexical sort:
SELECTenum_col
FROMtbl_name
ORDER BY CAST(enum_col
AS CHAR);
CAST()
also changes the result if
you use it as part of a more complex expression such as
CONCAT('Date: ',CAST(NOW() AS
DATE))
.
For temporal values, there is little need to use
CAST()
to extract data in different
formats. Instead, use a function such as
EXTRACT()
,
DATE_FORMAT()
, or
TIME_FORMAT()
. See
Section 12.6, “Date and Time Functions”.
To cast a string to a number, you normally need do nothing other than use the string value in numeric context:
mysql> SELECT 1+'1';
-> 2
That is also true for hexadecimal and bit literals, which are binary strings by default:
mysql>SELECT X'41', X'41'+0;
-> 'A', 65 mysql>SELECT b'1100001', b'1100001'+0;
-> 'a', 97
A string used in an arithmetic operation is converted to a floating-point number during expression evaluation.
A number used in string context is converted to a string:
mysql> SELECT CONCAT('hello you ',2);
-> 'hello you 2'
For information about implicit conversion of numbers to strings, see Section 12.2, “Type Conversion in Expression Evaluation”.
MySQL supports arithmetic with both signed and unsigned 64-bit
values. For numeric operators (such as
+
or
-
) where one of the
operands is an unsigned integer, the result is unsigned by default
(see Section 12.5.1, “Arithmetic Operators”). To override this,
use the SIGNED
or UNSIGNED
cast operator to cast a value to a signed or unsigned 64-bit
integer, respectively.
mysql>SELECT 1 - 2;
-> -1 mysql>SELECT CAST(1 - 2 AS UNSIGNED);
-> 18446744073709551615 mysql>SELECT CAST(CAST(1 - 2 AS UNSIGNED) AS SIGNED);
-> -1
If either operand is a floating-point value, the result is a
floating-point value and is not affected by the preceding rule.
(In this context, DECIMAL
column
values are regarded as floating-point values.)
mysql> SELECT CAST(1 AS UNSIGNED) - 2.0;
-> -1.0
The SQL mode affects the result of conversion operations (see Section 5.1.10, “Server SQL Modes”). Examples:
For conversion of a “zero” date string to a date,
CONVERT()
and
CAST()
return
NULL
and produce a warning when the
NO_ZERO_DATE
SQL mode is
enabled.
For integer subtraction, if the
NO_UNSIGNED_SUBTRACTION
SQL
mode is enabled, the subtraction result is signed even if any
operand is unsigned.
The following list describes the available cast functions and operators:
BINARY
expr
The BINARY
operator converts the
expression to a binary string (a string that has the
binary
character set and
binary
collation). A common use for
BINARY
is to force a character
string comparison to be done byte by byte using numeric byte
values rather than character by character. The
BINARY
operator also causes
trailing spaces in comparisons to be significant. For
information about the differences between the
binary
collation of the
binary
character set and the
_bin
collations of nonbinary character
sets, see Section 10.8.5, “The binary Collation Compared to _bin Collations”.
mysql>SELECT 'a' = 'A';
-> 1 mysql>SELECT BINARY 'a' = 'A';
-> 0 mysql>SELECT 'a' = 'a ';
-> 1 mysql>SELECT BINARY 'a' = 'a ';
-> 0
In a comparison, BINARY
affects
the entire operation; it can be given before either operand
with the same result.
To convert a string expression to a binary string, these constructs are equivalent:
BINARYexpr
CAST(expr
AS BINARY) CONVERT(expr
USING BINARY)
If a value is a string literal, it can be designated as a
binary string without performing any conversion by using the
_binary
character set introducer:
mysql>SELECT 'a' = 'A';
-> 1 mysql>SELECT _binary 'a' = 'A';
-> 0
For information about introducers, see Section 10.3.8, “Character Set Introducers”.
The BINARY
operator in
expressions differs in effect from the
BINARY
attribute in character column
definitions. A character column defined with the
BINARY
attribute is assigned the table
default character set and the binary (_bin
)
collation of that character set. Every nonbinary character set
has a _bin
collation. For example, if the
table default character set is utf8
, these
two column definitions are equivalent:
CHAR(10) BINARY CHAR(10) CHARACTER SET utf8 COLLATE utf8_bin
The use of CHARACTER SET binary
in the
definition of a CHAR
,
VARCHAR
, or
TEXT
column causes the column
to be treated as the corresponding binary string data type.
For example, the following pairs of definitions are
equivalent:
CHAR(10) CHARACTER SET binary BINARY(10) VARCHAR(10) CHARACTER SET binary VARBINARY(10) TEXT CHARACTER SET binary BLOB
The CAST()
function takes an
expression of any type and produces a result value of the
specified type, similar to
CONVERT()
. For more
information, see the description of
CONVERT()
.
CAST()
is standard SQL syntax.
CONVERT(
,
expr
,type
)CONVERT(
expr
USING transcoding_name
)
The CONVERT()
function takes an
expression of any type and produces a result value of the
specified type.
Discussion of
CONVERT(
syntax here also
applies to
expr
,
type
)CAST(
, which is
equivalent.
expr
AS
type
)
CONVERT(... USING ...)
is
standard SQL syntax. The non-USING
form of
CONVERT()
is ODBC syntax.
CONVERT()
with
USING
converts data between different
character sets. In MySQL, transcoding names are the same as
the corresponding character set names. For example, this
statement converts the string 'abc'
in the
default character set to the corresponding string in the
utf8
character set:
SELECT CONVERT('abc' USING utf8);
CONVERT()
without
USING
and
CAST()
take an expression and a
type
value specifying the result
type. These type
values are
permitted:
BINARY[(
N
)]
Produces a string with the
BINARY
data type. For a
description of how this affects comparisons, see
Section 11.3.3, “The BINARY and VARBINARY Types”. If the optional length
N
is given,
BINARY(
causes the cast to use no more than
N
)N
bytes of the argument. Values
shorter than N
bytes are padded
with 0x00
bytes to a length of
N
.
CHAR[(
N
)]
[charset_info
]
Produces a string with the
CHAR
data type. If the
optional length N
is given,
CHAR(
causes the cast to use no more than
N
)N
characters of the argument.
No padding occurs for values shorter than
N
characters.
With no charset_info
clause,
CHAR
produces a string with the default
character set. To specify the character set explicitly,
these charset_info
values are
permitted:
CHARACTER SET
:
Produces a string with the given character set.
charset_name
ASCII
: Shorthand for
CHARACTER SET latin1
.
UNICODE
: Shorthand for
CHARACTER SET ucs2
.
In all cases, the string has the character set default collation.
DATE
Produces a DATE
value.
DATETIME
Produces a DATETIME
value.
DECIMAL[(
M
[,D
])]
Produces a DECIMAL
value.
If the optional M
and
D
values are given, they
specify the maximum number of digits (the precision) and
the number of digits following the decimal point (the
scale).
JSON
Produces a JSON
value. For
details on the rules for conversion of values between
JSON
and other types, see
Comparison and Ordering of JSON Values.
NCHAR[(
N
)]
Like CHAR
, but produces a string with
the national character set. See
Section 10.3.7, “The National Character Set”.
Unlike CHAR
, NCHAR
does not permit trailing character set information to be
specified.
SIGNED [INTEGER]
Produces a signed integer value.
TIME
Produces a TIME
value.
UNSIGNED [INTEGER]
Produces an unsigned integer value.
Table 12.15 XML Functions
Name | Description |
---|---|
ExtractValue() |
Extract a value from an XML string using XPath notation |
UpdateXML() |
Return replaced XML fragment |
This section discusses XML and related functionality in MySQL.
It is possible to obtain XML-formatted output from MySQL in the
mysql and mysqldump
clients by invoking them with the
--xml
option. See
Section 4.5.1, “mysql — The MySQL Command-Line Client”, and Section 4.5.4, “mysqldump — A Database Backup Program”.
Two functions providing basic XPath 1.0 (XML Path Language, version 1.0) capabilities are available. Some basic information about XPath syntax and usage is provided later in this section; however, an in-depth discussion of these topics is beyond the scope of this manual, and you should refer to the XML Path Language (XPath) 1.0 standard for definitive information. A useful resource for those new to XPath or who desire a refresher in the basics is the Zvon.org XPath Tutorial, which is available in several languages.
These functions remain under development. We continue to improve these and other aspects of XML and XPath functionality in MySQL 5.7 and onwards. You may discuss these, ask questions about them, and obtain help from other users with them in the MySQL XML User Forum.
XPath expressions used with these functions support user variables and local stored program variables. User variables are weakly checked; variables local to stored programs are strongly checked (see also Bug #26518):
User variables (weak checking).
Variables using the syntax
$@
(that is, user variables) are not checked. No warnings or
errors are issued by the server if a variable has the wrong
type or has previously not been assigned a value. This also
means the user is fully responsible for any typographical
errors, since no warnings will be given if (for example)
variable_name
$@myvariable
is used where
$@myvariable
was intended.
Example:
mysql>SET @xml = '<a><b>X</b><b>Y</b></a>';
Query OK, 0 rows affected (0.00 sec) mysql>SET @i =1, @j = 2;
Query OK, 0 rows affected (0.00 sec) mysql>SELECT @i, ExtractValue(@xml, '//b[$@i]');
+------+--------------------------------+ | @i | ExtractValue(@xml, '//b[$@i]') | +------+--------------------------------+ | 1 | X | +------+--------------------------------+ 1 row in set (0.00 sec) mysql>SELECT @j, ExtractValue(@xml, '//b[$@j]');
+------+--------------------------------+ | @j | ExtractValue(@xml, '//b[$@j]') | +------+--------------------------------+ | 2 | Y | +------+--------------------------------+ 1 row in set (0.00 sec) mysql>SELECT @k, ExtractValue(@xml, '//b[$@k]');
+------+--------------------------------+ | @k | ExtractValue(@xml, '//b[$@k]') | +------+--------------------------------+ | NULL | | +------+--------------------------------+ 1 row in set (0.00 sec)
Variables in stored programs (strong checking).
Variables using the syntax
$
can be declared and used with these functions when they are
called inside stored programs. Such variables are local to
the stored program in which they are defined, and are
strongly checked for type and value.
variable_name
Example:
mysql>DELIMITER |
mysql>CREATE PROCEDURE myproc ()
->BEGIN
->DECLARE i INT DEFAULT 1;
->DECLARE xml VARCHAR(25) DEFAULT '<a>X</a><a>Y</a><a>Z</a>';
-> ->WHILE i < 4 DO
->SELECT xml, i, ExtractValue(xml, '//a[$i]');
->SET i = i+1;
->END WHILE;
->END |
Query OK, 0 rows affected (0.01 sec) mysql>DELIMITER ;
mysql>CALL myproc();
+--------------------------+---+------------------------------+ | xml | i | ExtractValue(xml, '//a[$i]') | +--------------------------+---+------------------------------+ | <a>X</a><a>Y</a><a>Z</a> | 1 | X | +--------------------------+---+------------------------------+ 1 row in set (0.00 sec) +--------------------------+---+------------------------------+ | xml | i | ExtractValue(xml, '//a[$i]') | +--------------------------+---+------------------------------+ | <a>X</a><a>Y</a><a>Z</a> | 2 | Y | +--------------------------+---+------------------------------+ 1 row in set (0.01 sec) +--------------------------+---+------------------------------+ | xml | i | ExtractValue(xml, '//a[$i]') | +--------------------------+---+------------------------------+ | <a>X</a><a>Y</a><a>Z</a> | 3 | Z | +--------------------------+---+------------------------------+ 1 row in set (0.01 sec)
Parameters. Variables used in XPath expressions inside stored routines that are passed in as parameters are also subject to strong checking.
Expressions containing user variables or variables local to stored programs must otherwise (except for notation) conform to the rules for XPath expressions containing variables as given in the XPath 1.0 specification.
A user variable used to store an XPath expression is treated as an empty string. Because of this, it is not possible to store an XPath expression as a user variable. (Bug #32911)
ExtractValue(
xml_frag
,
xpath_expr
)
ExtractValue()
takes two string
arguments, a fragment of XML markup
xml_frag
and an XPath expression
xpath_expr
(also known as a
locator); it returns the
text (CDATA
) of the first text node which
is a child of the element or elements matched by the XPath
expression.
Using this function is the equivalent of performing a match
using the xpath_expr
after
appending /text()
. In other words,
ExtractValue('<a><b>Sakila</b></a>',
'/a/b')
and
ExtractValue('<a><b>Sakila</b></a>',
'/a/b/text()')
produce the same result.
If multiple matches are found, the content of the first child text node of each matching element is returned (in the order matched) as a single, space-delimited string.
If no matching text node is found for the expression
(including the implicit /text()
)—for
whatever reason, as long as
xpath_expr
is valid, and
xml_frag
consists of elements which
are properly nested and closed—an empty string is
returned. No distinction is made between a match on an empty
element and no match at all. This is by design.
If you need to determine whether no matching element was found
in xml_frag
or such an element was
found but contained no child text nodes, you should test the
result of an expression that uses the XPath
count()
function. For example, both of
these statements return an empty string, as shown here:
mysql>SELECT ExtractValue('<a><b/></a>', '/a/b');
+-------------------------------------+ | ExtractValue('<a><b/></a>', '/a/b') | +-------------------------------------+ | | +-------------------------------------+ 1 row in set (0.00 sec) mysql>SELECT ExtractValue('<a><c/></a>', '/a/b');
+-------------------------------------+ | ExtractValue('<a><c/></a>', '/a/b') | +-------------------------------------+ | | +-------------------------------------+ 1 row in set (0.00 sec)
However, you can determine whether there was actually a matching element using the following:
mysql>SELECT ExtractValue('<a><b/></a>', 'count(/a/b)');
+-------------------------------------+ | ExtractValue('<a><b/></a>', 'count(/a/b)') | +-------------------------------------+ | 1 | +-------------------------------------+ 1 row in set (0.00 sec) mysql>SELECT ExtractValue('<a><c/></a>', 'count(/a/b)');
+-------------------------------------+ | ExtractValue('<a><c/></a>', 'count(/a/b)') | +-------------------------------------+ | 0 | +-------------------------------------+ 1 row in set (0.01 sec)
ExtractValue()
returns only
CDATA
, and does not return any tags that
might be contained within a matching tag, nor any of their
content (see the result returned as val1
in the following example).
mysql>SELECT
->ExtractValue('<a>ccc<b>ddd</b></a>', '/a') AS val1,
->ExtractValue('<a>ccc<b>ddd</b></a>', '/a/b') AS val2,
->ExtractValue('<a>ccc<b>ddd</b></a>', '//b') AS val3,
->ExtractValue('<a>ccc<b>ddd</b></a>', '/b') AS val4,
->ExtractValue('<a>ccc<b>ddd</b><b>eee</b></a>', '//b') AS val5;
+------+------+------+------+---------+ | val1 | val2 | val3 | val4 | val5 | +------+------+------+------+---------+ | ccc | ddd | ddd | | ddd eee | +------+------+------+------+---------+
This function uses the current SQL collation for making
comparisons with contains()
, performing the
same collation aggregation as other string functions (such as
CONCAT()
), in taking into
account the collation coercibility of their arguments; see
Section 10.8.4, “Collation Coercibility in Expressions”, for an
explanation of the rules governing this behavior.
(Previously, binary—that is, case-sensitive—comparison was always used.)
NULL
is returned if
xml_frag
contains elements which
are not properly nested or closed, and a warning is generated,
as shown in this example:
mysql>SELECT ExtractValue('<a>c</a><b', '//a');
+-----------------------------------+ | ExtractValue('<a>c</a><b', '//a') | +-----------------------------------+ | NULL | +-----------------------------------+ 1 row in set, 1 warning (0.00 sec) mysql>SHOW WARNINGS\G
*************************** 1. row *************************** Level: Warning Code: 1525 Message: Incorrect XML value: 'parse error at line 1 pos 11: END-OF-INPUT unexpected ('>' wanted)' 1 row in set (0.00 sec) mysql>SELECT ExtractValue('<a>c</a><b/>', '//a');
+-------------------------------------+ | ExtractValue('<a>c</a><b/>', '//a') | +-------------------------------------+ | c | +-------------------------------------+ 1 row in set (0.00 sec)
UpdateXML(
xml_target
,
xpath_expr
,
new_xml
)
This function replaces a single portion of a given fragment of
XML markup xml_target
with a new
XML fragment new_xml
, and then
returns the changed XML. The portion of
xml_target
that is replaced matches
an XPath expression xpath_expr
supplied by the user.
If no expression matching
xpath_expr
is found, or if multiple
matches are found, the function returns the original
xml_target
XML fragment. All three
arguments should be strings.
mysql>SELECT
->UpdateXML('<a><b>ccc</b><d></d></a>', '/a', '<e>fff</e>') AS val1,
->UpdateXML('<a><b>ccc</b><d></d></a>', '/b', '<e>fff</e>') AS val2,
->UpdateXML('<a><b>ccc</b><d></d></a>', '//b', '<e>fff</e>') AS val3,
->UpdateXML('<a><b>ccc</b><d></d></a>', '/a/d', '<e>fff</e>') AS val4,
->UpdateXML('<a><d></d><b>ccc</b><d></d></a>', '/a/d', '<e>fff</e>') AS val5
->\G
*************************** 1. row *************************** val1: <e>fff</e> val2: <a><b>ccc</b><d></d></a> val3: <a><e>fff</e><d></d></a> val4: <a><b>ccc</b><e>fff</e></a> val5: <a><d></d><b>ccc</b><d></d></a>
A discussion in depth of XPath syntax and usage are beyond the scope of this manual. Please see the XML Path Language (XPath) 1.0 specification for definitive information. A useful resource for those new to XPath or who are wishing a refresher in the basics is the Zvon.org XPath Tutorial, which is available in several languages.
Descriptions and examples of some basic XPath expressions follow:
/
tag
Matches
<
if
and only if
tag
/><
is
the root element.
tag
/>
Example: /a
has a match in
<a><b/></a>
because it
matches the outermost (root) tag. It does not match the inner
a
element in
<b><a/></b>
because in
this instance it is the child of another element.
/
tag1
/tag2
Matches
<
if
and only if it is a child of
tag2
/><
,
and
tag1
/><
is
the root element.
tag1
/>
Example: /a/b
matches the
b
element in the XML fragment
<a><b/></a>
because it is
a child of the root element a
. It
does not have a match in
<b><a/></b>
because in
this case, b
is the root element
(and hence the child of no other element). Nor does the XPath
expression have a match in
<a><c><b/></c></a>
;
here, b
is a descendant of
a
, but not actually a child of
a
.
This construct is extendable to three or more elements. For
example, the XPath expression /a/b/c
matches the c
element in the
fragment
<a><b><c/></b></a>
.
//
tag
Matches any instance of
<
.
tag
>
Example: //a
matches the
a
element in any of the following:
<a><b><c/></b></a>
;
<c><a><b/></a></b>
;
<c><b><a/></b></c>
.
//
can be combined with
/
. For example, //a/b
matches the b
element in either of
the fragments <a><b/></a>
or
<c><a><b/></a></c>
.
//
is the
equivalent of
tag
/descendant-or-self::*/
.
A common error is to confuse this with
tag
/descendant-or-self::
,
although the latter expression can actually lead to very
different results, as can be seen here:
tag
mysql>SET @xml = '<a><b><c>w</c><b>x</b><d>y</d>z</b></a>';
Query OK, 0 rows affected (0.00 sec) mysql>SELECT @xml;
+-----------------------------------------+ | @xml | +-----------------------------------------+ | <a><b><c>w</c><b>x</b><d>y</d>z</b></a> | +-----------------------------------------+ 1 row in set (0.00 sec) mysql>SELECT ExtractValue(@xml, '//b[1]');
+------------------------------+ | ExtractValue(@xml, '//b[1]') | +------------------------------+ | x z | +------------------------------+ 1 row in set (0.00 sec) mysql>SELECT ExtractValue(@xml, '//b[2]');
+------------------------------+ | ExtractValue(@xml, '//b[2]') | +------------------------------+ | | +------------------------------+ 1 row in set (0.01 sec) mysql>SELECT ExtractValue(@xml, '/descendant-or-self::*/b[1]');
+---------------------------------------------------+ | ExtractValue(@xml, '/descendant-or-self::*/b[1]') | +---------------------------------------------------+ | x z | +---------------------------------------------------+ 1 row in set (0.06 sec) mysql>SELECT ExtractValue(@xml, '/descendant-or-self::*/b[2]');
+---------------------------------------------------+ | ExtractValue(@xml, '/descendant-or-self::*/b[2]') | +---------------------------------------------------+ | | +---------------------------------------------------+ 1 row in set (0.00 sec) mysql>SELECT ExtractValue(@xml, '/descendant-or-self::b[1]');
+-------------------------------------------------+ | ExtractValue(@xml, '/descendant-or-self::b[1]') | +-------------------------------------------------+ | z | +-------------------------------------------------+ 1 row in set (0.00 sec) mysql>SELECT ExtractValue(@xml, '/descendant-or-self::b[2]');
+-------------------------------------------------+ | ExtractValue(@xml, '/descendant-or-self::b[2]') | +-------------------------------------------------+ | x | +-------------------------------------------------+ 1 row in set (0.00 sec)
The *
operator acts as a
“wildcard” that matches any element. For example,
the expression /*/b
matches the
b
element in either of the XML
fragments <a><b/></a>
or
<c><b/></c>
. However, the
expression does not produce a match in the fragment
<b><a/></b>
because
b
must be a child of some other
element. The wildcard may be used in any position: The
expression /*/b/*
will match any child of a
b
element that is itself not the
root element.
You can match any of several locators using the
|
(UNION
)
operator. For example, the expression
//b|//c
matches all
b
and c
elements in the XML target.
It is also possible to match an element based on the value of
one or more of its attributes. This done using the syntax
.
For example, the expression tag
[@attribute
="value
"]//b[@id="idB"]
matches the second b
element in the
fragment <a><b id="idA"/><c/><b
id="idB"/></a>
. To match against
any element having
,
use the XPath expression
attribute
="value
"//*[
.
attribute
="value
"]
To filter multiple attribute values, simply use multiple
attribute-comparison clauses in succession. For example, the
expression //b[@c="x"][@d="y"]
matches the
element <b c="x" d="y"/>
occurring
anywhere in a given XML fragment.
To find elements for which the same attribute matches any of
several values, you can use multiple locators joined by the
|
operator. For example, to match all
b
elements whose
c
attributes have either of the
values 23 or 17, use the expression
//b[@c="23"]|//b[@c="17"]
. You can also use
the logical or
operator for this purpose:
//b[@c="23" or @c="17"]
.
The difference between or
and
|
is that or
joins
conditions, while |
joins result sets.
XPath Limitations. The XPath syntax supported by these functions is currently subject to the following limitations:
Nodeset-to-nodeset comparison (such as
'/a/b[@c=@d]'
) is not supported.
All of the standard XPath comparison operators are supported. (Bug #22823)
Relative locator expressions are resolved in the context of the root node. For example, consider the following query and result:
mysql>SELECT ExtractValue(
->'<a><b c="1">X</b><b c="2">Y</b></a>',
->'a/b'
->) AS result;
+--------+ | result | +--------+ | X Y | +--------+ 1 row in set (0.03 sec)
In this case, the locator a/b
resolves to
/a/b
.
Relative locators are also supported within predicates. In the
following example, d[../@c="1"]
is resolved
as /a/b[@c="1"]/d
:
mysql>SELECT ExtractValue(
->'<a>
-><b c="1"><d>X</d></b>
-><b c="2"><d>X</d></b>
-></a>',
->'a/b/d[../@c="1"]')
->AS result;
+--------+ | result | +--------+ | X | +--------+ 1 row in set (0.00 sec)
Locators prefixed with expressions that evaluate as scalar values—including variable references, literals, numbers, and scalar function calls—are not permitted, and their use results in an error.
The ::
operator is not supported in
combination with node types such as the following:
axis
::comment()
axis
::text()
axis
::processing-instructions()
axis
::node()
However, name tests (such as
and axis
::name
) are
supported, as shown in these examples:
axis
::*
mysql>SELECT ExtractValue('<a><b>x</b><c>y</c></a>','/a/child::b');
+-------------------------------------------------------+ | ExtractValue('<a><b>x</b><c>y</c></a>','/a/child::b') | +-------------------------------------------------------+ | x | +-------------------------------------------------------+ 1 row in set (0.02 sec) mysql>SELECT ExtractValue('<a><b>x</b><c>y</c></a>','/a/child::*');
+-------------------------------------------------------+ | ExtractValue('<a><b>x</b><c>y</c></a>','/a/child::*') | +-------------------------------------------------------+ | x y | +-------------------------------------------------------+ 1 row in set (0.01 sec)
“Up-and-down” navigation is not supported in cases where the path would lead “above” the root element. That is, you cannot use expressions which match on descendants of ancestors of a given element, where one or more of the ancestors of the current element is also an ancestor of the root element (see Bug #16321).
The following XPath functions are not supported, or have known issues as indicated:
id()
lang()
local-name()
name()
namespace-uri()
normalize-space()
starts-with()
string()
substring-after()
substring-before()
translate()
The following axes are not supported:
following-sibling
following
preceding-sibling
preceding
XPath expressions passed as arguments to
ExtractValue()
and
UpdateXML()
may contain the colon
character (:
) in element selectors, which
enables their use with markup employing XML namespaces notation.
For example:
mysql>SET @xml = '<a>111<b:c>222<d>333</d><e:f>444</e:f></b:c></a>';
Query OK, 0 rows affected (0.00 sec) mysql>SELECT ExtractValue(@xml, '//e:f');
+-----------------------------+ | ExtractValue(@xml, '//e:f') | +-----------------------------+ | 444 | +-----------------------------+ 1 row in set (0.00 sec) mysql>SELECT UpdateXML(@xml, '//b:c', '<g:h>555</g:h>');
+--------------------------------------------+ | UpdateXML(@xml, '//b:c', '<g:h>555</g:h>') | +--------------------------------------------+ | <a>111<g:h>555</g:h></a> | +--------------------------------------------+ 1 row in set (0.00 sec)
This is similar in some respects to what is permitted by
Apache Xalan and
some other parsers, and is much simpler than requiring namespace
declarations or the use of the namespace-uri()
and local-name()
functions.
Error handling.
For both ExtractValue()
and
UpdateXML()
, the XPath locator
used must be valid and the XML to be searched must consist of
elements which are properly nested and closed. If the locator is
invalid, an error is generated:
mysql> SELECT ExtractValue('<a>c</a><b/>', '/&a');
ERROR 1105 (HY000): XPATH syntax error: '&a'
If xml_frag
does not consist of
elements which are properly nested and closed,
NULL
is returned and a warning is generated, as
shown in this example:
mysql>SELECT ExtractValue('<a>c</a><b', '//a');
+-----------------------------------+ | ExtractValue('<a>c</a><b', '//a') | +-----------------------------------+ | NULL | +-----------------------------------+ 1 row in set, 1 warning (0.00 sec) mysql>SHOW WARNINGS\G
*************************** 1. row *************************** Level: Warning Code: 1525 Message: Incorrect XML value: 'parse error at line 1 pos 11: END-OF-INPUT unexpected ('>' wanted)' 1 row in set (0.00 sec) mysql>SELECT ExtractValue('<a>c</a><b/>', '//a');
+-------------------------------------+ | ExtractValue('<a>c</a><b/>', '//a') | +-------------------------------------+ | c | +-------------------------------------+ 1 row in set (0.00 sec)
The replacement XML used as the third argument to
UpdateXML()
is
not checked to determine whether it
consists solely of elements which are properly nested and
closed.
XPath Injection. code injection occurs when malicious code is introduced into the system to gain unauthorized access to privileges and data. It is based on exploiting assumptions made by developers about the type and content of data input from users. XPath is no exception in this regard.
A common scenario in which this can happen is the case of application which handles authorization by matching the combination of a login name and password with those found in an XML file, using an XPath expression like this one:
//user[login/text()='neapolitan' and password/text()='1c3cr34m']/attribute::id
This is the XPath equivalent of an SQL statement like this one:
SELECT id FROM users WHERE login='neapolitan' AND password='1c3cr34m';
A PHP application employing XPath might handle the login process like this:
<?php $file = "users.xml"; $login = $POST["login"]; $password = $POST["password"]; $xpath = "//user[login/text()=$login and password/text()=$password]/attribute::id"; if( file_exists($file) ) { $xml = simplexml_load_file($file); if($result = $xml->xpath($xpath)) echo "You are now logged in as user $result[0]."; else echo "Invalid login name or password."; } else exit("Failed to open $file."); ?>
No checks are performed on the input. This means that a malevolent
user can “short-circuit” the test by entering
' or 1=1
for both the login name and password,
resulting in $xpath
being evaluated as shown
here:
//user[login/text()='' or 1=1 and password/text()='' or 1=1]/attribute::id
Since the expression inside the square brackets always evaluates
as true
, it is effectively the same as this
one, which matches the id
attribute of every
user
element in the XML document:
//user/attribute::id
One way in which this particular attack can be circumvented is
simply by quoting the variable names to be interpolated in the
definition of $xpath
, forcing the values passed
from a Web form to be converted to strings:
$xpath = "//user[login/text()='$login' and password/text()='$password']/attribute::id";
This is the same strategy that is often recommended for preventing SQL injection attacks. In general, the practices you should follow for preventing XPath injection attacks are the same as for preventing SQL injection:
Never accepted untested data from users in your application.
Check all user-submitted data for type; reject or convert data that is of the wrong type
Test numeric data for out of range values; truncate, round, or reject values that are out of range. Test strings for illegal characters and either strip them out or reject input containing them.
Do not output explicit error messages that might provide an unauthorized user with clues that could be used to compromise the system; log these to a file or database table instead.
Just as SQL injection attacks can be used to obtain information about database schemas, so can XPath injection be used to traverse XML files to uncover their structure, as discussed in Amit Klein's paper Blind XPath Injection (PDF file, 46KB).
It is also important to check the output being sent back to the
client. Consider what can happen when we use the MySQL
ExtractValue()
function:
mysql>SELECT ExtractValue(
->LOAD_FILE('users.xml'),
->'//user[login/text()="" or 1=1 and password/text()="" or 1=1]/attribute::id'
->) AS id;
+-------------------------------+ | id | +-------------------------------+ | 00327 13579 02403 42354 28570 | +-------------------------------+ 1 row in set (0.01 sec)
Because ExtractValue()
returns
multiple matches as a single space-delimited string, this
injection attack provides every valid ID contained within
users.xml
to the user as a single row of
output. As an extra safeguard, you should also test output before
returning it to the user. Here is a simple example:
mysql>SELECT @id = ExtractValue(
->LOAD_FILE('users.xml'),
->'//user[login/text()="" or 1=1 and password/text()="" or 1=1]/attribute::id'
->);
Query OK, 0 rows affected (0.00 sec) mysql>SELECT IF(
->INSTR(@id, ' ') = 0,
->@id,
->'Unable to retrieve user ID')
->AS singleID;
+----------------------------+ | singleID | +----------------------------+ | Unable to retrieve user ID | +----------------------------+ 1 row in set (0.00 sec)
In general, the guidelines for returning data to users securely are the same as for accepting user input. These can be summed up as:
Always test outgoing data for type and permissible values.
Never permit unauthorized users to view error messages that might provide information about the application that could be used to exploit it.
Bit functions and operators comprise
BIT_COUNT()
,
BIT_AND()
,
BIT_OR()
,
BIT_XOR()
,
&
,
|
,
^
,
~
,
<<
, and
>>
.
(The BIT_AND()
,
BIT_OR()
, and
BIT_XOR()
functions are aggregate
functions described at Section 12.20.1, “Aggregate (GROUP BY) Function Descriptions”.)
Currently, bit functions and operators require
BIGINT
(64-bit integer) arguments
and return BIGINT
values, so they
have a maximum range of 64 bits. Arguments of other types are
converted to BIGINT
and truncation
might occur.
An extension for MySQL 8.0 changes this
cast-to-BIGINT
behavior: Bit
functions and operators permit binary string type arguments
(BINARY
,
VARBINARY
, and the
BLOB
types), enabling them to take
arguments and produce return values larger than 64 bits.
Consequently, bit operations on binary arguments in MySQL 5.7
might produce different results in MySQL 8.0. To provide advance
notice about this potential change in behavior, the server
produces warnings as of MySQL 5.7.11 for bit operations for which
binary arguments are not converted to integer in MySQL 8.0. These
warnings afford an opportunity to rewrite affected statements. To
explicitly produce MySQL 5.7 behavior in a way that will not
change after an upgrade to 8.0, cast bit-operation binary
arguments to convert them to integer.
The five problematic expression types to watch out for are:
nonliteral_binary
{ & | ^ }binary
binary
{ & | ^ }nonliteral_binary
nonliteral_binary
{ << >> }anything
~nonliteral_binary
AGGR_BIT_FUNC
(nonliteral_binary
)
Those expressions return BIGINT
in
MySQL 5.7, binary string in 8.0.
Explanation of notation:
{
: List of
operators that apply to the given expression type.
op1
op2
... }
binary
: Any kind of binary string
argument, including a hexadecimal literal, bit literal, or
NULL
literal.
nonliteral_binary
: An argument that
is a binary string value other than a hexadecimal literal, bit
literal, or NULL
literal.
AGGR_BIT_FUNC
: An aggregate
function that takes bit-value arguments:
BIT_AND()
,
BIT_OR()
,
BIT_XOR()
.
The server produces a single warning for each problematic expression in a statement, not a warning for each row processed. Suppose that a statement containing two problematic expressions selects three rows from a table. The number of warnings per statement execution is two, not six. The following example illustrates this.
mysql>CREATE TABLE t(vbin1 VARBINARY(32), vbin2 VARBINARY(32));
Query OK, 0 rows affected (0.03 sec) mysql>INSERT INTO t VALUES (3,1), (3,2), (3,3);
Query OK, 3 rows affected (0.01 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql>SELECT HEX(vbin1 & vbin2) AS op1,
->HEX(vbin1 | vbin2) AS op2
->FROM t;
+------+------+ | op1 | op2 | +------+------+ | 1 | 3 | | 2 | 3 | | 3 | 3 | +------+------+ 3 rows in set, 2 warnings (0.00 sec) mysql>SHOW WARNINGS\G
*************************** 1. row *************************** Level: Warning Code: 1287 Message: Bitwise operations on BINARY will change behavior in a future version, check the 'Bit functions' section in the manual. *************************** 2. row *************************** Level: Warning Code: 1287 Message: Bitwise operations on BINARY will change behavior in a future version, check the 'Bit functions' section in the manual. 2 rows in set (0.00 sec)
To avoid having an affected statement produce a different result
after an upgrade to MySQL 8.0, rewrite it so that it generates no
bit-operation warnings. To do this, cast at least one binary
argument to BIGINT
with
CAST(... AS UNSIGNED)
. This makes
the MySQL 5.7 implicit binary-to-integer cast explicit:
mysql>SELECT HEX(CAST(vbin1 AS UNSIGNED) & CAST(vbin2 AS UNSIGNED)) AS op1,
->HEX(CAST(vbin1 AS UNSIGNED) | CAST(vbin2 AS UNSIGNED)) AS op2
->FROM t;
+------+------+ | op1 | op2 | +------+------+ | 1 | 3 | | 2 | 3 | | 3 | 3 | +------+------+ 3 rows in set (0.01 sec) mysql>SHOW WARNINGS\G
Empty set (0.00 sec)
With the statement rewritten as shown, MySQL 8.0 respects the intention to treat the binary arguments as integers and produces the same result as in 5.7. Also, replicating the statement from MySQL 5.7 to 8.0 does not produce different results on different servers.
An affected statement that cannot be rewritten is subject to these potential problems with respect to upgrades and replication:
The statement might return a different result after an upgrade to MySQL 8.0.
Replication to MySQL 8.0 from older versions might fail for statement-based and mixed-format binary logging. This is also true for replaying older binary logs on an 8.0 server (for example, using mysqlbinlog). To avoid this, switch to row-based binary logging on the older master server.
The following list describes available bit functions and operators:
Bitwise OR.
The result is an unsigned 64-bit integer.
mysql> SELECT 29 | 15;
-> 31
Bitwise AND.
The result is an unsigned 64-bit integer.
mysql> SELECT 29 & 15;
-> 13
Bitwise XOR.
The result is an unsigned 64-bit integer.
mysql>SELECT 1 ^ 1;
-> 0 mysql>SELECT 1 ^ 0;
-> 1 mysql>SELECT 11 ^ 3;
-> 8
Shifts a longlong (BIGINT
)
number to the left.
The result is an unsigned 64-bit integer. The value is truncated to 64 bits. In particular, if the shift count is greater or equal to the width of an unsigned 64-bit number, the result is zero.
mysql> SELECT 1 << 2;
-> 4
Shifts a longlong (BIGINT
)
number to the right.
The result is an unsigned 64-bit integer. The value is truncated to 64 bits. In particular, if the shift count is greater or equal to the width of an unsigned 64-bit number, the result is zero.
mysql> SELECT 4 >> 2;
-> 1
Invert all bits.
The result is an unsigned 64-bit integer.
mysql> SELECT 5 & ~1;
-> 4
Returns the number of bits that are set in the argument
N
as an unsigned 64-bit integer, or
NULL
if the argument is
NULL
.
mysql> SELECT BIT_COUNT(29), BIT_COUNT(b'101010');
-> 4, 3
Table 12.17 Encryption Functions
Name | Description |
---|---|
AES_DECRYPT() |
Decrypt using AES |
AES_ENCRYPT() |
Encrypt using AES |
ASYMMETRIC_DECRYPT() |
Decrypt ciphertext using private or public key |
ASYMMETRIC_DERIVE() |
Derive symmetric key from asymmetric keys |
ASYMMETRIC_ENCRYPT() |
Encrypt cleartext using private or public key |
ASYMMETRIC_SIGN() |
Generate signature from digest |
ASYMMETRIC_VERIFY() |
Verify that signature matches digest |
COMPRESS() |
Return result as a binary string |
CREATE_ASYMMETRIC_PRIV_KEY() |
Create private key |
CREATE_ASYMMETRIC_PUB_KEY() |
Create public key |
CREATE_DH_PARAMETERS() |
Generate shared DH secret |
CREATE_DIGEST() |
Generate digest from string |
DECODE() (deprecated) |
Decode a string encrypted using ENCODE() |
DES_DECRYPT() (deprecated) |
Decrypt a string |
DES_ENCRYPT() (deprecated) |
Encrypt a string |
ENCODE() (deprecated) |
Encode a string |
ENCRYPT() (deprecated) |
Encrypt a string |
MD5() |
Calculate MD5 checksum |
PASSWORD() (deprecated) |
Calculate and return a password string |
RANDOM_BYTES() |
Return a random byte vector |
SHA1() , SHA() |
Calculate an SHA-1 160-bit checksum |
SHA2() |
Calculate an SHA-2 checksum |
UNCOMPRESS() |
Uncompress a string compressed |
UNCOMPRESSED_LENGTH() |
Return the length of a string before compression |
VALIDATE_PASSWORD_STRENGTH() |
Determine strength of password |
Many encryption and compression functions return strings for which
the result might contain arbitrary byte values. If you want to
store these results, use a column with a
VARBINARY
or
BLOB
binary string data type. This
will avoid potential problems with trailing space removal or
character set conversion that would change data values, such as
may occur if you use a nonbinary string data type
(CHAR
,
VARCHAR
,
TEXT
).
Some encryption functions return strings of ASCII characters:
MD5()
,
PASSWORD()
,
SHA()
,
SHA1()
,
SHA2()
. Their return value is a
string that has a character set and collation determined by the
character_set_connection
and
collation_connection
system
variables. This is a nonbinary string unless the character set is
binary
.
If an application stores values from a function such as
MD5()
or
SHA1()
that returns a string of hex
digits, more efficient storage and comparisons can be obtained by
converting the hex representation to binary using
UNHEX()
and storing the result in a
BINARY(
column. Each pair of hexadecimal digits requires one byte in
binary form, so the value of N
)N
depends
on the length of the hex string. N
is
16 for an MD5()
value and 20 for a
SHA1()
value. For
SHA2()
,
N
ranges from 28 to 32 depending on the
argument specifying the desired bit length of the result.
The size penalty for storing the hex string in a
CHAR
column is at least two times,
up to eight times if the value is stored in a column that uses the
utf8
character set (where each character uses 4
bytes). Storing the string also results in slower comparisons
because of the larger values and the need to take character set
collation rules into account.
Suppose that an application stores
MD5()
string values in a
CHAR(32)
column:
CREATE TABLE md5_tbl (md5_val CHAR(32), ...); INSERT INTO md5_tbl (md5_val, ...) VALUES(MD5('abcdef'), ...);
To convert hex strings to more compact form, modify the
application to use UNHEX()
and
BINARY(16)
instead as follows:
CREATE TABLE md5_tbl (md5_val BINARY(16), ...); INSERT INTO md5_tbl (md5_val, ...) VALUES(UNHEX(MD5('abcdef')), ...);
Applications should be prepared to handle the very rare case that a hashing function produces the same value for two different input values. One way to make collisions detectable is to make the hash column a primary key.
Exploits for the MD5 and SHA-1 algorithms have become known. You
may wish to consider using another one-way encryption function
described in this section instead, such as
SHA2()
.
Passwords or other sensitive values supplied as arguments to encryption functions are sent as cleartext to the MySQL server unless an SSL connection is used. Also, such values will appear in any MySQL logs to which they are written. To avoid these types of exposure, applications can encrypt sensitive values on the client side before sending them to the server. The same considerations apply to encryption keys. To avoid exposing these, applications can use stored procedures to encrypt and decrypt values on the server side.
AES_DECRYPT(
crypt_str
,key_str
[,init_vector
])
This function decrypts data using the official AES (Advanced
Encryption Standard) algorithm. For more information, see the
description of AES_ENCRYPT()
.
Statements that use
AES_DECRYPT()
are unsafe for
statement-based replication and cannot be stored in the query
cache.
AES_ENCRYPT(
str
,key_str
[,init_vector
])
AES_ENCRYPT()
and
AES_DECRYPT()
implement
encryption and decryption of data using the official AES
(Advanced Encryption Standard) algorithm, previously known as
“Rijndael.” The AES standard permits various key
lengths. By default these functions implement AES with a
128-bit key length. Key lengths of 196 or 256 bits can be
used, as described later. The key length is a trade off
between performance and security.
AES_ENCRYPT()
encrypts the
string str
using the key string
key_str
and returns a binary string
containing the encrypted output.
AES_DECRYPT()
decrypts the
encrypted string crypt_str
using
the key string key_str
and returns
the original plaintext string. If either function argument is
NULL
, the function returns
NULL
.
The str
and
crypt_str
arguments can be any
length, and padding is automatically added to
str
so it is a multiple of a block
as required by block-based algorithms such as AES. This
padding is automatically removed by the
AES_DECRYPT()
function. The
length of crypt_str
can be
calculated using this formula:
16 * (trunc(string_length
/ 16) + 1)
For a key length of 128 bits, the most secure way to pass a
key to the key_str
argument is to
create a truly random 128-bit value and pass it as a binary
value. For example:
INSERT INTO t VALUES (1,AES_ENCRYPT('text',UNHEX('F3229A0B371ED2D9441B830D21A390C3')));
A passphrase can be used to generate an AES key by hashing the passphrase. For example:
INSERT INTO t VALUES (1,AES_ENCRYPT('text', UNHEX(SHA2('My secret passphrase',512))));
Do not pass a password or passphrase directly to
crypt_str
, hash it first. Previous
versions of this documentation suggested the former approach,
but it is no longer recommended as the examples shown here are
more secure.
If AES_DECRYPT()
detects
invalid data or incorrect padding, it returns
NULL
. However, it is possible for
AES_DECRYPT()
to return a
non-NULL
value (possibly garbage) if the
input data or the key is invalid.
AES_ENCRYPT()
and
AES_DECRYPT()
permit control of
the block encryption mode and take an optional
init_vector
initialization vector
argument:
The block_encryption_mode
system variable controls the mode for block-based
encryption algorithms. Its default value is
aes-128-ecb
, which signifies encryption
using a key length of 128 bits and ECB mode. For a
description of the permitted values of this variable, see
Section 5.1.7, “Server System Variables”.
The optional init_vector
argument provides an initialization vector for block
encryption modes that require it.
For modes that require the optional
init_vector
argument, it must be 16
bytes or longer (bytes in excess of 16 are ignored). An error
occurs if init_vector
is missing.
For modes that do not require
init_vector
, it is ignored and a
warning is generated if it is specified.
A random string of bytes to use for the initialization vector
can be produced by calling
RANDOM_BYTES(16)
. For
encryption modes that require an initialization vector, the
same vector must be used for encryption and decryption.
mysql>SET block_encryption_mode = 'aes-256-cbc';
mysql>SET @key_str = SHA2('My secret passphrase',512);
mysql>SET @init_vector = RANDOM_BYTES(16);
mysql>SET @crypt_str = AES_ENCRYPT('text',@key_str,@init_vector);
mysql>SELECT AES_DECRYPT(@crypt_str,@key_str,@init_vector);
+-----------------------------------------------+ | AES_DECRYPT(@crypt_str,@key_str,@init_vector) | +-----------------------------------------------+ | text | +-----------------------------------------------+
The following table lists each permitted block encryption mode, the SSL libraries that support it, and whether the initialization vector argument is required.
Block Encryption Mode | SSL Libraries that Support Mode | Initialization Vector Required |
---|---|---|
ECB | OpenSSL, yaSSL | No |
CBC | OpenSSL, yaSSL | Yes |
CFB1 | OpenSSL | Yes |
CFB8 | OpenSSL | Yes |
CFB128 | OpenSSL | Yes |
OFB | OpenSSL | Yes |
Statements that use
AES_ENCRYPT()
or
AES_DECRYPT()
are unsafe for
statement-based replication and cannot be stored in the query
cache.
Compresses a string and returns the result as a binary string.
This function requires MySQL to have been compiled with a
compression library such as zlib
.
Otherwise, the return value is always NULL
.
The compressed string can be uncompressed with
UNCOMPRESS()
.
mysql>SELECT LENGTH(COMPRESS(REPEAT('a',1000)));
-> 21 mysql>SELECT LENGTH(COMPRESS(''));
-> 0 mysql>SELECT LENGTH(COMPRESS('a'));
-> 13 mysql>SELECT LENGTH(COMPRESS(REPEAT('a',16)));
-> 15
The compressed string contents are stored the following way:
Empty strings are stored as empty strings.
Nonempty strings are stored as a 4-byte length of the
uncompressed string (low byte first), followed by the
compressed string. If the string ends with space, an extra
.
character is added to avoid problems
with endspace trimming should the result be stored in a
CHAR
or
VARCHAR
column. (However,
use of nonbinary string data types such as
CHAR
or
VARCHAR
to store compressed
strings is not recommended anyway because character set
conversion may occur. Use a
VARBINARY
or
BLOB
binary string column
instead.)
DECODE()
decrypts the encrypted
string crypt_str
using
pass_str
as the password.
crypt_str
should be a string
returned from ENCODE()
.
The ENCODE()
and
DECODE()
functions are
deprecated in MySQL 5.7, will be removed in a
future MySQL release, and should no longer be used. Consider
using AES_ENCRYPT()
and
AES_DECRYPT()
instead.
DES_DECRYPT(
crypt_str
[,key_str
])
Decrypts a string encrypted with
DES_ENCRYPT()
. If an error
occurs, this function returns NULL
.
This function works only if MySQL has been configured with SSL support. See Section 6.3, “Using Encrypted Connections”.
If no key_str
argument is given,
DES_DECRYPT()
examines the
first byte of the encrypted string to determine the DES key
number that was used to encrypt the original string, and then
reads the key from the DES key file to decrypt the message.
For this to work, the user must have the
SUPER
privilege. The key file
can be specified with the
--des-key-file
server option.
If you pass this function a key_str
argument, that string is used as the key for decrypting the
message.
If the crypt_str
argument does not
appear to be an encrypted string, MySQL returns the given
crypt_str
.
The DES_ENCRYPT()
and
DES_DECRYPT()
functions are
deprecated as of MySQL 5.7.6, will be removed in a future
MySQL release, and should no longer be used. Consider using
AES_ENCRYPT()
and
AES_DECRYPT()
instead.
DES_ENCRYPT(
str
[,{key_num
|key_str
}])
Encrypts the string with the given key using the Triple-DES algorithm.
This function works only if MySQL has been configured with SSL support. See Section 6.3, “Using Encrypted Connections”.
The encryption key to use is chosen based on the second
argument to DES_ENCRYPT()
, if
one was given. With no argument, the first key from the DES
key file is used. With a key_num
argument, the given key number (0 to 9) from the DES key file
is used. With a key_str
argument,
the given key string is used to encrypt
str
.
The key file can be specified with the
--des-key-file
server option.
The return string is a binary string where the first character
is CHAR(128 |
. If an error
occurs, key_num
)DES_ENCRYPT()
returns
NULL
.
The 128 is added to make it easier to recognize an encrypted
key. If you use a string key,
key_num
is 127.
The string length for the result is given by this formula:
new_len
=orig_len
+ (8 - (orig_len
% 8)) + 1
Each line in the DES key file has the following format:
key_num
des_key_str
Each key_num
value must be a number
in the range from 0
to
9
. Lines in the file may be in any order.
des_key_str
is the string that is
used to encrypt the message. There should be at least one
space between the number and the key. The first key is the
default key that is used if you do not specify any key
argument to DES_ENCRYPT()
.
You can tell MySQL to read new key values from the key file
with the FLUSH DES_KEY_FILE
statement. This requires the
RELOAD
privilege.
One benefit of having a set of default keys is that it gives applications a way to check for the existence of encrypted column values, without giving the end user the right to decrypt those values.
The DES_ENCRYPT()
and
DES_DECRYPT()
functions are
deprecated as of MySQL 5.7.6, will be removed in a future
MySQL release, and should no longer be used. Consider using
AES_ENCRYPT()
and
AES_DECRYPT()
instead.
mysql>SELECT customer_address FROM customer_table
>WHERE crypted_credit_card = DES_ENCRYPT('credit_card_number');
ENCODE()
encrypts
str
using
pass_str
as the password. The
result is a binary string of the same length as
str
. To decrypt the result, use
DECODE()
.
The ENCODE()
and
DECODE()
functions are
deprecated in MySQL 5.7, will be removed in a
future MySQL release, and should no longer be used.
If you still need to use
ENCODE()
, a salt value must be
used with it to reduce risk. For example:
ENCODE('cleartext', CONCAT('my_random_salt','my_secret_password'))
A new random salt value must be used whenever a password is updated.
Encrypts str
using the Unix
crypt()
system call and returns a binary
string. The salt
argument must be a
string with at least two characters or the result will be
NULL
. If no salt
argument is given, a random value is used.
The ENCRYPT()
function is
deprecated as of MySQL 5.7.6, will be removed in a future
MySQL release, and should no longer be used. For one-way
hashing, consider using
SHA2()
instead.
mysql> SELECT ENCRYPT('hello');
-> 'VxuFAJXVARROc'
ENCRYPT()
ignores all but the
first eight characters of str
, at
least on some systems. This behavior is determined by the
implementation of the underlying crypt()
system call.
The use of ENCRYPT()
with the
ucs2
, utf16
,
utf16le
, or utf32
multibyte character sets is not recommended because the system
call expects a string terminated by a zero byte.
If crypt()
is not available on your
system (as is the case with Windows),
ENCRYPT()
always returns
NULL
.
Calculates an MD5 128-bit checksum for the string. The value
is returned as a string of 32 hexadecimal digits, or
NULL
if the argument was
NULL
. The return value can, for example, be
used as a hash key. See the notes at the beginning of this
section about storing hash values efficiently.
The return value is a string in the connection character set.
mysql> SELECT MD5('testing');
-> 'ae2b1fca515949e5d54fb22b8ed95575'
This is the “RSA Data Security, Inc. MD5 Message-Digest Algorithm.”
See the note regarding the MD5 algorithm at the beginning this section.
This function is deprecated as of MySQL 5.7.6 and will be removed in a future MySQL release.
Returns a hashed password string calculated from the cleartext
password str
. The return value is a
string in the connection character set, or
NULL
if the argument is
NULL
. This function is the SQL interface to
the algorithm used by the server to encrypt MySQL passwords
for storage in the mysql.user
grant table.
The old_passwords
system
variable controls the password hashing method used by the
PASSWORD()
function. It also
influences password hashing performed by
CREATE USER
and
GRANT
statements that specify a
password using an IDENTIFIED BY
clause.
The following table shows, for each password hashing method,
the permitted value of old_passwords
and
which authentication plugins use the hashing method.
Password Hashing Method | old_passwords Value | Associated Authentication Plugin |
---|---|---|
MySQL 4.1 native hashing | 0 | mysql_native_password |
SHA-256 hashing | 2 | sha256_password |
SHA-256 password hashing
(old_passwords=2
) uses a
random salt value, which makes the result from
PASSWORD()
nondeterministic.
Consequently, statements that use this function are not safe
for statement-based replication and cannot be stored in the
query cache.
Encryption performed by
PASSWORD()
is one-way (not
reversible), but it is not the same type of encryption used
for Unix passwords.
PASSWORD()
is used by the
authentication system in MySQL Server; you should
not use it in your own applications.
For that purpose, consider a more secure function such as
SHA2()
instead. Also see
RFC 2195,
section 2 (Challenge-Response Authentication Mechanism
(CRAM)), for more information about handling
passwords and authentication securely in your applications.
Under some circumstances, statements that invoke
PASSWORD()
may be recorded in
server logs or on the client side in a history file such as
~/.mysql_history
, which means that
cleartext passwords may be read by anyone having read access
to that information. For information about the conditions
under which this occurs for the server logs and how to
control it, see Section 6.1.2.3, “Passwords and Logging”. For
similar information about client-side logging, see
Section 4.5.1.3, “mysql Client Logging”.
This function returns a binary string of
len
random bytes generated using
the random number generator of the SSL library. Permitted
values of len
range from 1 to 1024.
For values outside that range, an error occurs.
RANDOM_BYTES()
can be used to
provide the initialization vector for the
AES_DECRYPT()
and
AES_ENCRYPT()
functions. For
use in that context, len
must be at
least 16. Larger values are permitted, but bytes in excess of
16 are ignored.
RANDOM_BYTES()
generates a
random value, which makes its result nondeterministic.
Consequently, statements that use this function are unsafe for
statement-based replication and cannot be stored in the query
cache.
Calculates an SHA-1 160-bit checksum for the string, as
described in RFC 3174 (Secure Hash Algorithm). The value is
returned as a string of 40 hexadecimal digits, or
NULL
if the argument was
NULL
. One of the possible uses for this
function is as a hash key. See the notes at the beginning of
this section about storing hash values efficiently.
SHA()
is
synonymous with SHA1()
.
The return value is a string in the connection character set.
mysql> SELECT SHA1('abc');
-> 'a9993e364706816aba3e25717850c26c9cd0d89d'
SHA1()
can be considered a
cryptographically more secure equivalent of
MD5()
. However, see the note
regarding the MD5 and SHA-1 algorithms at the beginning this
section.
Calculates the SHA-2 family of hash functions (SHA-224,
SHA-256, SHA-384, and SHA-512). The first argument is the
plaintext string to be hashed. The second argument indicates
the desired bit length of the result, which must have a value
of 224, 256, 384, 512, or 0 (which is equivalent to 256). If
either argument is NULL
or the hash length
is not one of the permitted values, the return value is
NULL
. Otherwise, the function result is a
hash value containing the desired number of bits. See the
notes at the beginning of this section about storing hash
values efficiently.
The return value is a string in the connection character set.
mysql> SELECT SHA2('abc', 224);
-> '23097d223405d8228642a477bda255b32aadbce4bda0b3f7e36c9da7'
This function works only if MySQL has been configured with SSL support. See Section 6.3, “Using Encrypted Connections”.
SHA2()
can be considered
cryptographically more secure than
MD5()
or
SHA1()
.
UNCOMPRESS(
string_to_uncompress
)
Uncompresses a string compressed by the
COMPRESS()
function. If the
argument is not a compressed value, the result is
NULL
. This function requires MySQL to have
been compiled with a compression library such as
zlib
. Otherwise, the return value is always
NULL
.
mysql>SELECT UNCOMPRESS(COMPRESS('any string'));
-> 'any string' mysql>SELECT UNCOMPRESS('any string');
-> NULL
UNCOMPRESSED_LENGTH(
compressed_string
)
Returns the length that the compressed string had before being compressed.
mysql> SELECT UNCOMPRESSED_LENGTH(COMPRESS(REPEAT('a',30)));
-> 30
VALIDATE_PASSWORD_STRENGTH(
str
)
Given an argument representing a plaintext password, this function returns an integer to indicate how strong the password is. The return value ranges from 0 (weak) to 100 (strong).
Password assessment by
VALIDATE_PASSWORD_STRENGTH()
is
done by the validate_password
plugin. If
that plugin is not installed, the function always returns 0.
For information about installing
validate_password
, see
Section 6.4.3, “The Password Validation Plugin”. To examine or configure
the parameters that affect password testing, check or set the
system variables implemented by
validate_password
. See
Section 6.4.3.2, “Password Validation Plugin Options and Variables”.
The password is subjected to increasingly strict tests and the
return value reflects which tests were satisfied, as shown in
the following table. In addition, if the
validate_password_check_user_name
system variable is enabled and the password matches the user
name,
VALIDATE_PASSWORD_STRENGTH()
returns 0 regardless of how other
validate_password
system variables are set.
Password Test | Return Value |
---|---|
Length < 4 | 0 |
Length ≥ 4 and <
validate_password_length |
25 |
Satisfies policy 1 (LOW ) |
50 |
Satisfies policy 2 (MEDIUM ) |
75 |
Satisfies policy 3 (STRONG ) |
100 |
This section describes functions used to manipulate user-level locks.
Table 12.18 Locking Functions
Name | Description |
---|---|
GET_LOCK() |
Get a named lock |
IS_FREE_LOCK() |
Whether the named lock is free |
IS_USED_LOCK() |
Whether the named lock is in use; return connection identifier if true |
RELEASE_ALL_LOCKS() |
Release all current named locks |
RELEASE_LOCK() |
Release the named lock |
Tries to obtain a lock with a name given by the string
str
, using a timeout of
timeout
seconds. A negative
timeout
value means infinite
timeout. The lock is exclusive. While held by one session,
other sessions cannot obtain a lock of the same name.
Returns 1
if the lock was obtained
successfully, 0
if the attempt timed out
(for example, because another client has previously locked the
name), or NULL
if an error occurred (such
as running out of memory or the thread was killed with
mysqladmin kill).
A lock obtained with GET_LOCK()
is released explicitly by executing
RELEASE_LOCK()
or implicitly
when your session terminates (either normally or abnormally).
Locks obtained with GET_LOCK()
are not released when transactions commit or roll back.
In MySQL 5.7, GET_LOCK()
was
reimplemented using the metadata locking (MDL) subsystem and
its capabilities were extended. Multiple simultaneous locks
can be acquired and GET_LOCK()
does not release any existing locks.
It is even possible for a given session to acquire multiple locks for the same name. Other sessions cannot acquire a lock with that name until the acquiring session releases all its locks for the name.
As a result of the MDL reimplementation, uniquely named locks
acquired with GET_LOCK()
appear
in the Performance Schema
metadata_locks
table. The
OBJECT_TYPE
column says USER LEVEL
LOCK
and the OBJECT_NAME
column
indicates the lock name. In the case that multiple locks are
acquired for the same name, only the
first lock for the name registers a row in the
metadata_locks
table. Subsequent
locks for the name increment a counter in the lock but do not
acquire additional metadata locks. The
metadata_locks
row for the lock
is deleted when the last lock instance on the name is
released.
The capability of acquiring multiple locks means there is the
possibility of deadlock among clients. When this happens, the
server chooses a caller and terminates its lock-acquisition
request with an
ER_USER_LOCK_DEADLOCK
error.
This error does not cause transactions to roll back.
Before MySQL 5.7, only a single simultaneous lock can be
acquired and GET_LOCK()
releases any existing lock. The difference in lock acquisition
behavior as of MySQL 5.7 can be seen by the following example.
Suppose that you execute these statements:
SELECT GET_LOCK('lock1',10); SELECT GET_LOCK('lock2',10); SELECT RELEASE_LOCK('lock2'); SELECT RELEASE_LOCK('lock1');
In MySQL 5.7 or later, the second
GET_LOCK()
acquires a second
lock and both RELEASE_LOCK()
calls return 1 (success). Before MySQL 5.7, the second
GET_LOCK()
releases the first
lock ('lock1')
and the second
RELEASE_LOCK()
returns
NULL
(failure) because there is no
'lock1'
to release.
MySQL 5.7 and later enforces a maximum length on lock names of 64 characters. Previously, no limit was enforced.
GET_LOCK()
can be used to
implement application locks or to simulate record locks. Names
are locked on a server-wide basis. If a name has been locked
within one session, GET_LOCK()
blocks any request by another session for a lock with the same
name. This enables clients that agree on a given lock name to
use the name to perform cooperative advisory locking. But be
aware that it also enables a client that is not among the set
of cooperating clients to lock a name, either inadvertently or
deliberately, and thus prevent any of the cooperating clients
from locking that name. One way to reduce the likelihood of
this is to use lock names that are database-specific or
application-specific. For example, use lock names of the form
db_name.str
or
app_name.str
.
If multiple clients are waiting for a lock, the order in which they will acquire it is undefined. Applications should not assume that clients will acquire the lock in the same order that they issued the lock requests.
GET_LOCK()
is unsafe for
statement-based replication. A warning is logged if you use
this function when
binlog_format
is set to
STATEMENT
.
With the capability of acquiring multiple named locks in MySQL 5.7, it is possible for a single statement to acquire a large number of locks. For example:
INSERT INTO ... SELECT GET_LOCK(t1.col_name) FROM t1;
These types of statements may have certain adverse effects. For example, if the statement fails part way through and rolls back, locks acquired up to the point of failure will still exist. If the intent is for there to be a correspondence between rows inserted and locks acquired, that intent will not be satisfied. Also, if it is important that locks are granted in a certain order, be aware that result set order may differ depending on which execution plan the optimizer chooses. For these reasons, it may be best to limit applications to a single lock-acquisition call per statement.
A different locking interface is available as either a plugin
service or a set of user-defined functions. This interface
provides lock namespaces and distinct read and write locks,
unlike the interface provided by
GET_LOCK()
and related
functions. For details, see Section 28.3.1, “The Locking Service”.
Checks whether the lock named str
is free to use (that is, not locked). Returns
1
if the lock is free (no one is using the
lock), 0
if the lock is in use, and
NULL
if an error occurs (such as an
incorrect argument).
This function is unsafe for statement-based replication. A
warning is logged if you use this function when
binlog_format
is set to
STATEMENT
.
Checks whether the lock named str
is in use (that is, locked). If so, it returns the connection
identifier of the client session that holds the lock.
Otherwise, it returns NULL
.
This function is unsafe for statement-based replication. A
warning is logged if you use this function when
binlog_format
is set to
STATEMENT
.
Releases all named locks held by the current session and returns the number of locks released (0 if there were none)
This function is unsafe for statement-based replication. A
warning is logged if you use this function when
binlog_format
is set to
STATEMENT
.
Releases the lock named by the string
str
that was obtained with
GET_LOCK()
. Returns
1
if the lock was released,
0
if the lock was not established by this
thread (in which case the lock is not released), and
NULL
if the named lock did not exist. The
lock does not exist if it was never obtained by a call to
GET_LOCK()
or if it has
previously been released.
The DO
statement is convenient
to use with RELEASE_LOCK()
. See
Section 13.2.3, “DO Statement”.
This function is unsafe for statement-based replication. A
warning is logged if you use this function when
binlog_format
is set to
STATEMENT
.
Table 12.19 Information Functions
Name | Description |
---|---|
BENCHMARK() |
Repeatedly execute an expression |
CHARSET() |
Return the character set of the argument |
COERCIBILITY() |
Return the collation coercibility value of the string argument |
COLLATION() |
Return the collation of the string argument |
CONNECTION_ID() |
Return the connection ID (thread ID) for the connection |
CURRENT_USER() , CURRENT_USER |
The authenticated user name and host name |
DATABASE() |
Return the default (current) database name |
FOUND_ROWS() |
For a SELECT with a LIMIT clause, the number of rows that would be returned were there no LIMIT clause |
LAST_INSERT_ID() |
Value of the AUTOINCREMENT column for the last INSERT |
ROW_COUNT() |
The number of rows updated |
SCHEMA() |
Synonym for DATABASE() |
SESSION_USER() |
Synonym for USER() |
SYSTEM_USER() |
Synonym for USER() |
USER() |
The user name and host name provided by the client |
VERSION() |
Return a string that indicates the MySQL server version |
The BENCHMARK()
function
executes the expression expr
repeatedly count
times. It may be
used to time how quickly MySQL processes the expression. The
result value is 0
, or
NULL
for inappropriate arguments such as a
NULL
or negative repeat count.
The intended use is from within the mysql client, which reports query execution times:
mysql> SELECT BENCHMARK(1000000,AES_ENCRYPT('hello','goodbye'));
+---------------------------------------------------+
| BENCHMARK(1000000,AES_ENCRYPT('hello','goodbye')) |
+---------------------------------------------------+
| 0 |
+---------------------------------------------------+
1 row in set (4.74 sec)
The time reported is elapsed time on the client end, not CPU
time on the server end. It is advisable to execute
BENCHMARK()
several times, and
to interpret the result with regard to how heavily loaded the
server machine is.
BENCHMARK()
is intended for
measuring the runtime performance of scalar expressions, which
has some significant implications for the way that you use it
and interpret the results:
Only scalar expressions can be used. Although the
expression can be a subquery, it must return a single
column and at most a single row. For example,
BENCHMARK(10, (SELECT * FROM
t))
will fail if the table t
has more than one column or more than one row.
Executing a SELECT
statement
expr
N
times differs from executing
SELECT BENCHMARK(
in terms of the
amount of overhead involved. The two have very different
execution profiles and you should not expect them to take
the same amount of time. The former involves the parser,
optimizer, table locking, and runtime evaluation
N
,
expr
)N
times each. The latter
involves only runtime evaluation
N
times, and all the other
components just once. Memory structures already allocated
are reused, and runtime optimizations such as local
caching of results already evaluated for aggregate
functions can alter the results. Use of
BENCHMARK()
thus measures
performance of the runtime component by giving more weight
to that component and removing the “noise”
introduced by the network, parser, optimizer, and so
forth.
Returns the character set of the string argument.
mysql>SELECT CHARSET('abc');
-> 'latin1' mysql>SELECT CHARSET(CONVERT('abc' USING utf8));
-> 'utf8' mysql>SELECT CHARSET(USER());
-> 'utf8'
Returns the collation coercibility value of the string argument.
mysql>SELECT COERCIBILITY('abc' COLLATE latin1_swedish_ci);
-> 0 mysql>SELECT COERCIBILITY(USER());
-> 3 mysql>SELECT COERCIBILITY('abc');
-> 4 mysql>SELECT COERCIBILITY(1000);
-> 5
The return values have the meanings shown in the following table. Lower values have higher precedence.
Coercibility | Meaning | Example |
---|---|---|
0 |
Explicit collation | Value with COLLATE clause |
1 |
No collation | Concatenation of strings with different collations |
2 |
Implicit collation | Column value, stored routine parameter or local variable |
3 |
System constant | USER() return value |
4 |
Coercible | Literal string |
5 |
Numeric | Numeric or temporal value |
5 |
Ignorable | NULL or an expression derived from
NULL |
For more information, see Section 10.8.4, “Collation Coercibility in Expressions”.
Returns the collation of the string argument.
mysql>SELECT COLLATION('abc');
-> 'latin1_swedish_ci' mysql>SELECT COLLATION(_utf8'abc');
-> 'utf8_general_ci'
Returns the connection ID (thread ID) for the connection. Every connection has an ID that is unique among the set of currently connected clients.
The value returned by
CONNECTION_ID()
is the same
type of value as displayed in the ID
column
of the
INFORMATION_SCHEMA.PROCESSLIST
table, the Id
column of
SHOW PROCESSLIST
output, and
the PROCESSLIST_ID
column of the
Performance Schema threads
table.
mysql> SELECT CONNECTION_ID();
-> 23786
Returns the user name and host name combination for the MySQL
account that the server used to authenticate the current
client. This account determines your access privileges. The
return value is a string in the utf8
character set.
The value of CURRENT_USER()
can
differ from the value of
USER()
.
mysql>SELECT USER();
-> 'davida@localhost' mysql>SELECT * FROM mysql.user;
ERROR 1044: Access denied for user ''@'localhost' to database 'mysql' mysql>SELECT CURRENT_USER();
-> '@localhost'
The example illustrates that although the client specified a
user name of davida
(as indicated by the
value of the USER()
function),
the server authenticated the client using an anonymous user
account (as seen by the empty user name part of the
CURRENT_USER()
value). One way
this might occur is that there is no account listed in the
grant tables for davida
.
Within a stored program or view,
CURRENT_USER()
returns the
account for the user who defined the object (as given by its
DEFINER
value) unless defined with the
SQL SECURITY INVOKER
characteristic. In the
latter case, CURRENT_USER()
returns the object's invoker.
Triggers and events have no option to define the SQL
SECURITY
characteristic, so for these objects,
CURRENT_USER()
returns the
account for the user who defined the object. To return the
invoker, use USER()
or
SESSION_USER()
.
The following statements support use of the
CURRENT_USER()
function to take
the place of the name of (and, possibly, a host for) an
affected user or a definer; in such cases,
CURRENT_USER()
is expanded
where and as needed:
For information about the implications that this expansion of
CURRENT_USER()
has for
replication, see
Section 16.4.1.8, “Replication of CURRENT_USER()”.
Returns the default (current) database name as a string in the
utf8
character set. If there is no default
database, DATABASE()
returns
NULL
. Within a stored routine, the default
database is the database that the routine is associated with,
which is not necessarily the same as the database that is the
default in the calling context.
mysql> SELECT DATABASE();
-> 'test'
If there is no default database,
DATABASE()
returns
NULL
.
A SELECT
statement may include
a LIMIT
clause to restrict the number of
rows the server returns to the client. In some cases, it is
desirable to know how many rows the statement would have
returned without the LIMIT
, but without
running the statement again. To obtain this row count, include
an SQL_CALC_FOUND_ROWS
option in the
SELECT
statement, and then
invoke FOUND_ROWS()
afterward:
mysql>SELECT SQL_CALC_FOUND_ROWS * FROM
->tbl_name
WHERE id > 100 LIMIT 10;
mysql>SELECT FOUND_ROWS();
The second SELECT
returns a
number indicating how many rows the first
SELECT
would have returned had
it been written without the LIMIT
clause.
In the absence of the SQL_CALC_FOUND_ROWS
option in the most recent successful
SELECT
statement,
FOUND_ROWS()
returns the number
of rows in the result set returned by that statement. If the
statement includes a LIMIT
clause,
FOUND_ROWS()
returns the number
of rows up to the limit. For example,
FOUND_ROWS()
returns 10 or 60,
respectively, if the statement includes LIMIT
10
or LIMIT 50, 10
.
The row count available through
FOUND_ROWS()
is transient and
not intended to be available past the statement following the
SELECT SQL_CALC_FOUND_ROWS
statement. If
you need to refer to the value later, save it:
mysql>SELECT SQL_CALC_FOUND_ROWS * FROM ... ;
mysql>SET @rows = FOUND_ROWS();
If you are using SELECT
SQL_CALC_FOUND_ROWS
, MySQL must calculate how many
rows are in the full result set. However, this is faster than
running the query again without LIMIT
,
because the result set need not be sent to the client.
SQL_CALC_FOUND_ROWS
and
FOUND_ROWS()
can be useful in
situations when you want to restrict the number of rows that a
query returns, but also determine the number of rows in the
full result set without running the query again. An example is
a Web script that presents a paged display containing links to
the pages that show other sections of a search result. Using
FOUND_ROWS()
enables you to
determine how many other pages are needed for the rest of the
result.
The use of SQL_CALC_FOUND_ROWS
and
FOUND_ROWS()
is more complex
for UNION
statements than for
simple SELECT
statements,
because LIMIT
may occur at multiple places
in a UNION
. It may be applied
to individual SELECT
statements
in the UNION
, or global to the
UNION
result as a whole.
The intent of SQL_CALC_FOUND_ROWS
for
UNION
is that it should return
the row count that would be returned without a global
LIMIT
. The conditions for use of
SQL_CALC_FOUND_ROWS
with
UNION
are:
The SQL_CALC_FOUND_ROWS
keyword must
appear in the first SELECT
of the UNION
.
The value of FOUND_ROWS()
is exact only if
UNION ALL
is used. If UNION
without
ALL
is used, duplicate removal occurs
and the value of
FOUND_ROWS()
is only
approximate.
If no LIMIT
is present in the
UNION
,
SQL_CALC_FOUND_ROWS
is ignored and
returns the number of rows in the temporary table that is
created to process the
UNION
.
Beyond the cases described here, the behavior of
FOUND_ROWS()
is undefined (for
example, its value following a
SELECT
statement that fails
with an error).
FOUND_ROWS()
is not
replicated reliably using statement-based replication. This
function is automatically replicated using row-based
replication.
LAST_INSERT_ID()
,
LAST_INSERT_ID(
expr
)
With no argument,
LAST_INSERT_ID()
returns a
BIGINT UNSIGNED
(64-bit) value representing
the first automatically generated value successfully inserted
for an AUTO_INCREMENT
column as a result of
the most recently executed
INSERT
statement. The value of
LAST_INSERT_ID()
remains
unchanged if no rows are successfully inserted.
With an argument,
LAST_INSERT_ID()
returns an
unsigned integer.
For example, after inserting a row that generates an
AUTO_INCREMENT
value, you can get the value
like this:
mysql> SELECT LAST_INSERT_ID();
-> 195
The currently executing statement does not affect the value of
LAST_INSERT_ID()
. Suppose that
you generate an AUTO_INCREMENT
value with
one statement, and then refer to
LAST_INSERT_ID()
in a
multiple-row INSERT
statement
that inserts rows into a table with its own
AUTO_INCREMENT
column. The value of
LAST_INSERT_ID()
will remain
stable in the second statement; its value for the second and
later rows is not affected by the earlier row insertions.
(However, if you mix references to
LAST_INSERT_ID()
and
LAST_INSERT_ID(
,
the effect is undefined.)
expr
)
If the previous statement returned an error, the value of
LAST_INSERT_ID()
is undefined.
For transactional tables, if the statement is rolled back due
to an error, the value of
LAST_INSERT_ID()
is left
undefined. For manual
ROLLBACK
,
the value of LAST_INSERT_ID()
is not restored to that before the transaction; it remains as
it was at the point of the
ROLLBACK
.
Within the body of a stored routine (procedure or function) or
a trigger, the value of
LAST_INSERT_ID()
changes the
same way as for statements executed outside the body of these
kinds of objects. The effect of a stored routine or trigger
upon the value of
LAST_INSERT_ID()
that is seen
by following statements depends on the kind of routine:
If a stored procedure executes statements that change the
value of LAST_INSERT_ID()
,
the changed value is seen by statements that follow the
procedure call.
For stored functions and triggers that change the value, the value is restored when the function or trigger ends, so following statements will not see a changed value.
The ID that was generated is maintained in the server on a
per-connection basis. This means that the
value returned by the function to a given client is the first
AUTO_INCREMENT
value generated for most
recent statement affecting an
AUTO_INCREMENT
column by that
client. This value cannot be affected by other
clients, even if they generate
AUTO_INCREMENT
values of their own. This
behavior ensures that each client can retrieve its own ID
without concern for the activity of other clients, and without
the need for locks or transactions.
The value of LAST_INSERT_ID()
is not changed if you set the
AUTO_INCREMENT
column of a row to a
non-“magic” value (that is, a value that is not
NULL
and not 0
).
If you insert multiple rows using a single
INSERT
statement,
LAST_INSERT_ID()
returns the
value generated for the first inserted
row only. The reason for this is to
make it possible to reproduce easily the same
INSERT
statement against some
other server.
For example:
mysql>USE test;
mysql>CREATE TABLE t (
id INT AUTO_INCREMENT NOT NULL PRIMARY KEY,
name VARCHAR(10) NOT NULL
);
mysql>INSERT INTO t VALUES (NULL, 'Bob');
mysql>SELECT * FROM t;
+----+------+ | id | name | +----+------+ | 1 | Bob | +----+------+ mysql>SELECT LAST_INSERT_ID();
+------------------+ | LAST_INSERT_ID() | +------------------+ | 1 | +------------------+ mysql>INSERT INTO t VALUES
(NULL, 'Mary'), (NULL, 'Jane'), (NULL, 'Lisa');
mysql>SELECT * FROM t;
+----+------+ | id | name | +----+------+ | 1 | Bob | | 2 | Mary | | 3 | Jane | | 4 | Lisa | +----+------+ mysql>SELECT LAST_INSERT_ID();
+------------------+ | LAST_INSERT_ID() | +------------------+ | 2 | +------------------+
Although the second INSERT
statement inserted three new rows into t
,
the ID generated for the first of these rows was
2
, and it is this value that is returned by
LAST_INSERT_ID()
for the
following SELECT
statement.
If you use INSERT
IGNORE
and the row is ignored, the
LAST_INSERT_ID()
remains
unchanged from the current value (or 0 is returned if the
connection has not yet performed a successful
INSERT
) and, for non-transactional tables,
the AUTO_INCREMENT
counter is not
incremented. For InnoDB
tables, the
AUTO_INCREMENT
counter is incremented if
innodb_autoinc_lock_mode
is
set to 1
or 2
, as
demonstrated in the following example:
mysql>USE test;
mysql>SELECT @@innodb_autoinc_lock_mode;
+----------------------------+ | @@innodb_autoinc_lock_mode | +----------------------------+ | 1 | +----------------------------+ mysql>CREATE TABLE `t` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`val` INT(11) DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `i1` (`val`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
# Insert two rows mysql>INSERT INTO t (val) VALUES (1),(2);
# With auto_increment_offset=1, the inserted rows # result in an AUTO_INCREMENT value of 3 mysql>SHOW CREATE TABLE t\G
*************************** 1. row *************************** Table: t Create Table: CREATE TABLE `t` ( `id` int(11) NOT NULL AUTO_INCREMENT, `val` int(11) DEFAULT NULL, PRIMARY KEY (`id`), UNIQUE KEY `i1` (`val`) ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1 # LAST_INSERT_ID() returns the first automatically generated # value that is successfully inserted for the AUTO_INCREMENT column mysql>SELECT LAST_INSERT_ID();
+------------------+ | LAST_INSERT_ID() | +------------------+ | 1 | +------------------+ # The attempted insertion of duplicate rows fail but errors are ignored mysql>INSERT IGNORE INTO t (val) VALUES (1),(2);
Query OK, 0 rows affected (0.00 sec) Records: 2 Duplicates: 2 Warnings: 0 # With innodb_autoinc_lock_mode=1, the AUTO_INCREMENT counter # is incremented for the ignored rows mysql>SHOW CREATE TABLE t\G
*************************** 1. row *************************** Table: t Create Table: CREATE TABLE `t` ( `id` int(11) NOT NULL AUTO_INCREMENT, `val` int(11) DEFAULT NULL, PRIMARY KEY (`id`), UNIQUE KEY `i1` (`val`) ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=latin1 # The LAST_INSERT_ID is unchanged because the previous insert was unsuccessful mysql>SELECT LAST_INSERT_ID();
+------------------+ | LAST_INSERT_ID() | +------------------+ | 1 | +------------------+
For more information, see Section 14.6.1.6, “AUTO_INCREMENT Handling in InnoDB”.
If expr
is given as an argument to
LAST_INSERT_ID()
, the value of
the argument is returned by the function and is remembered as
the next value to be returned by
LAST_INSERT_ID()
. This can be
used to simulate sequences:
Create a table to hold the sequence counter and initialize it:
mysql>CREATE TABLE sequence (id INT NOT NULL);
mysql>INSERT INTO sequence VALUES (0);
Use the table to generate sequence numbers like this:
mysql>UPDATE sequence SET id=LAST_INSERT_ID(id+1);
mysql>SELECT LAST_INSERT_ID();
The UPDATE
statement
increments the sequence counter and causes the next call
to LAST_INSERT_ID()
to
return the updated value. The
SELECT
statement retrieves
that value. The
mysql_insert_id()
C API
function can also be used to get the value. See
Section 27.7.6.38, “mysql_insert_id()”.
You can generate sequences without calling
LAST_INSERT_ID()
, but the
utility of using the function this way is that the ID value is
maintained in the server as the last automatically generated
value. It is multi-user safe because multiple clients can
issue the UPDATE
statement and
get their own sequence value with the
SELECT
statement (or
mysql_insert_id()
), without
affecting or being affected by other clients that generate
their own sequence values.
Note that mysql_insert_id()
is
only updated after INSERT
and
UPDATE
statements, so you
cannot use the C API function to retrieve the value for
LAST_INSERT_ID(
after executing other SQL statements like
expr
)SELECT
or
SET
.
ROW_COUNT()
returns a value as follows:
DDL statements: 0. This applies to statements such as
CREATE TABLE
or
DROP TABLE
.
DML statements other than
SELECT
: The number of
affected rows. This applies to statements such as
UPDATE
,
INSERT
, or
DELETE
(as before), but now
also to statements such as ALTER
TABLE
and LOAD
DATA
.
SELECT
: -1 if the statement
returns a result set, or the number of rows
“affected” if it does not. For example, for
SELECT * FROM t1
,
ROW_COUNT()
returns -1. For
SELECT * FROM t1 INTO OUTFILE
'
,
file_name
'ROW_COUNT()
returns the
number of rows written to the file.
SIGNAL
statements: 0.
For UPDATE
statements, the
affected-rows value by default is the number of rows actually
changed. If you specify the
CLIENT_FOUND_ROWS
flag to
mysql_real_connect()
when
connecting to mysqld, the affected-rows
value is the number of rows “found”; that is,
matched by the WHERE
clause.
For REPLACE
statements, the
affected-rows value is 2 if the new row replaced an old row,
because in this case, one row was inserted after the duplicate
was deleted.
For
INSERT
... ON DUPLICATE KEY UPDATE
statements, the
affected-rows value per row is 1 if the row is inserted as a
new row, 2 if an existing row is updated, and 0 if an existing
row is set to its current values. If you specify the
CLIENT_FOUND_ROWS
flag, the affected-rows
value is 1 (not 0) if an existing row is set to its current
values.
The ROW_COUNT()
value is
similar to the value from the
mysql_affected_rows()
C API
function and the row count that the mysql
client displays following statement execution.
mysql>INSERT INTO t VALUES(1),(2),(3);
Query OK, 3 rows affected (0.00 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql>SELECT ROW_COUNT();
+-------------+ | ROW_COUNT() | +-------------+ | 3 | +-------------+ 1 row in set (0.00 sec) mysql>DELETE FROM t WHERE i IN(1,2);
Query OK, 2 rows affected (0.00 sec) mysql>SELECT ROW_COUNT();
+-------------+ | ROW_COUNT() | +-------------+ | 2 | +-------------+ 1 row in set (0.00 sec)
ROW_COUNT()
is not replicated
reliably using statement-based replication. This function is
automatically replicated using row-based replication.
This function is a synonym for
DATABASE()
.
SESSION_USER()
is a synonym for
USER()
.
SYSTEM_USER()
is a synonym for
USER()
.
Returns the current MySQL user name and host name as a string
in the utf8
character set.
mysql> SELECT USER();
-> 'davida@localhost'
The value indicates the user name you specified when
connecting to the server, and the client host from which you
connected. The value can be different from that of
CURRENT_USER()
.
Returns a string that indicates the MySQL server version. The
string uses the utf8
character set. The
value might have a suffix in addition to the version number.
See the description of the
version
system variable in
Section 5.1.7, “Server System Variables”.
This function is unsafe for statement-based replication. A
warning is logged if you use this function when
binlog_format
is set to
STATEMENT
.
mysql> SELECT VERSION();
-> '5.7.30-standard'
MySQL provides functions to perform various operations on spatial data. These functions can be grouped into several major categories according to the type of operation they perform:
Functions that create geometries in various formats (WKT, WKB, internal)
Functions that convert geometries between formats
Functions that access qualitative or quantitative properties of a geometry
Functions that describe relations between two geometries
Functions that create new geometries from existing ones
For general background about MySQL support for using spatial data, see Section 11.4, “Spatial Data Types”.
The following table lists each spatial function and provides a short description of each one.
Table 12.20 Spatial Functions
Name | Description |
---|---|
Area() (deprecated) |
Return Polygon or MultiPolygon area |
AsBinary() , AsWKB() (deprecated) |
Convert from internal geometry format to WKB |
AsText() , AsWKT() (deprecated) |
Convert from internal geometry format to WKT |
Buffer() (deprecated) |
Return geometry of points within given distance from geometry |
Centroid() (deprecated) |
Return centroid as a point |
Contains() (deprecated) |
Whether MBR of one geometry contains MBR of another |
ConvexHull() (deprecated) |
Return convex hull of geometry |
Crosses() (deprecated) |
Whether one geometry crosses another |
Dimension() (deprecated) |
Dimension of geometry |
Disjoint() (deprecated) |
Whether MBRs of two geometries are disjoint |
Distance() (deprecated) |
The distance of one geometry from another |
EndPoint() (deprecated) |
End Point of LineString |
Envelope() (deprecated) |
Return MBR of geometry |
Equals() (deprecated) |
Whether MBRs of two geometries are equal |
ExteriorRing() (deprecated) |
Return exterior ring of Polygon |
GeomCollFromText() , GeometryCollectionFromText() (deprecated) |
Return geometry collection from WKT |
GeomCollFromWKB() , GeometryCollectionFromWKB() (deprecated) |
Return geometry collection from WKB |
GeometryCollection() |
Construct geometry collection from geometries |
GeometryN() (deprecated) |
Return N-th geometry from geometry collection |
GeometryType() (deprecated) |
Return name of geometry type |
GeomFromText() , GeometryFromText() (deprecated) |
Return geometry from WKT |
GeomFromWKB() , GeometryFromWKB() (deprecated) |
Return geometry from WKB |
GLength() (deprecated) |
Return length of LineString |
InteriorRingN() (deprecated) |
Return N-th interior ring of Polygon |
Intersects() (deprecated) |
Whether MBRs of two geometries intersect |
IsClosed() (deprecated) |
Whether a geometry is closed and simple |
IsEmpty() (deprecated) |
Placeholder function |
IsSimple() (deprecated) |
Whether a geometry is simple |
LineFromText() , LineStringFromText() (deprecated) |
Construct LineString from WKT |
LineFromWKB() , LineStringFromWKB() (deprecated) |
Construct LineString from WKB |
LineString() |
Construct LineString from Point values |
MBRContains() |
Whether MBR of one geometry contains MBR of another |
MBRCoveredBy() |
Whether one MBR is covered by another |
MBRCovers() |
Whether one MBR covers another |
MBRDisjoint() |
Whether MBRs of two geometries are disjoint |
MBREqual() (deprecated) |
Whether MBRs of two geometries are equal |
MBREquals() |
Whether MBRs of two geometries are equal |
MBRIntersects() |
Whether MBRs of two geometries intersect |
MBROverlaps() |
Whether MBRs of two geometries overlap |
MBRTouches() |
Whether MBRs of two geometries touch |
MBRWithin() |
Whether MBR of one geometry is within MBR of another |
MLineFromText() , MultiLineStringFromText() (deprecated) |
Construct MultiLineString from WKT |
MLineFromWKB() , MultiLineStringFromWKB() (deprecated) |
Construct MultiLineString from WKB |
MPointFromText() , MultiPointFromText() (deprecated) |
Construct MultiPoint from WKT |
MPointFromWKB() , MultiPointFromWKB() (deprecated) |
Construct MultiPoint from WKB |
MPolyFromText() , MultiPolygonFromText() (deprecated) |
Construct MultiPolygon from WKT |
MPolyFromWKB() , MultiPolygonFromWKB() (deprecated) |
Construct MultiPolygon from WKB |
MultiLineString() |
Contruct MultiLineString from LineString values |
MultiPoint() |
Construct MultiPoint from Point values |
MultiPolygon() |
Construct MultiPolygon from Polygon values |
NumGeometries() (deprecated) |
Return number of geometries in geometry collection |
NumInteriorRings() (deprecated) |
Return number of interior rings in Polygon |
NumPoints() (deprecated) |
Return number of points in LineString |
Overlaps() (deprecated) |
Whether MBRs of two geometries overlap |
Point() |
Construct Point from coordinates |
PointFromText() (deprecated) |
Construct Point from WKT |
PointFromWKB() (deprecated) |
Construct Point from WKB |
PointN() (deprecated) |
Return N-th point from LineString |
PolyFromText() , PolygonFromText() (deprecated) |
Construct Polygon from WKT |
PolyFromWKB() , PolygonFromWKB() (deprecated) |
Construct Polygon from WKB |
Polygon() |
Construct Polygon from LineString arguments |
SRID() (deprecated) |
Return spatial reference system ID for geometry |
ST_Area() |
Return Polygon or MultiPolygon area |
ST_AsBinary() , ST_AsWKB() |
Convert from internal geometry format to WKB |
ST_AsGeoJSON() |
Generate GeoJSON object from geometry |
ST_AsText() , ST_AsWKT() |
Convert from internal geometry format to WKT |
ST_Buffer() |
Return geometry of points within given distance from geometry |
ST_Buffer_Strategy() |
Produce strategy option for ST_Buffer() |
ST_Centroid() |
Return centroid as a point |
ST_Contains() |
Whether one geometry contains another |
ST_ConvexHull() |
Return convex hull of geometry |
ST_Crosses() |
Whether one geometry crosses another |
ST_Difference() |
Return point set difference of two geometries |
ST_Dimension() |
Dimension of geometry |
ST_Disjoint() |
Whether one geometry is disjoint from another |
ST_Distance() |
The distance of one geometry from another |
ST_Distance_Sphere() |
Minimum distance on earth between two geometries |
ST_EndPoint() |
End Point of LineString |
ST_Envelope() |
Return MBR of geometry |
ST_Equals() |
Whether one geometry is equal to another |
ST_ExteriorRing() |
Return exterior ring of Polygon |
ST_GeoHash() |
Produce a geohash value |
ST_GeomCollFromText() , ST_GeometryCollectionFromText() , ST_GeomCollFromTxt() |
Return geometry collection from WKT |
ST_GeomCollFromWKB() , ST_GeometryCollectionFromWKB() |
Return geometry collection from WKB |
ST_GeometryN() |
Return N-th geometry from geometry collection |
ST_GeometryType() |
Return name of geometry type |
ST_GeomFromGeoJSON() |
Generate geometry from GeoJSON object |
ST_GeomFromText() , ST_GeometryFromText() |
Return geometry from WKT |
ST_GeomFromWKB() , ST_GeometryFromWKB() |
Return geometry from WKB |
ST_InteriorRingN() |
Return N-th interior ring of Polygon |
ST_Intersection() |
Return point set intersection of two geometries |
ST_Intersects() |
Whether one geometry intersects another |
ST_IsClosed() |
Whether a geometry is closed and simple |
ST_IsEmpty() |
Placeholder function |
ST_IsSimple() |
Whether a geometry is simple |
ST_IsValid() |
Whether a geometry is valid |
ST_LatFromGeoHash() |
Return latitude from geohash value |
ST_Length() |
Return length of LineString |
ST_LineFromText() , ST_LineStringFromText() |
Construct LineString from WKT |
ST_LineFromWKB() , ST_LineStringFromWKB() |
Construct LineString from WKB |
ST_LongFromGeoHash() |
Return longitude from geohash value |
ST_MakeEnvelope() |
Rectangle around two points |
ST_MLineFromText() , ST_MultiLineStringFromText() |
Construct MultiLineString from WKT |
ST_MLineFromWKB() , ST_MultiLineStringFromWKB() |
Construct MultiLineString from WKB |
ST_MPointFromText() , ST_MultiPointFromText() |
Construct MultiPoint from WKT |
ST_MPointFromWKB() , ST_MultiPointFromWKB() |
Construct MultiPoint from WKB |
ST_MPolyFromText() , ST_MultiPolygonFromText() |
Construct MultiPolygon from WKT |
ST_MPolyFromWKB() , ST_MultiPolygonFromWKB() |
Construct MultiPolygon from WKB |
ST_NumGeometries() |
Return number of geometries in geometry collection |
ST_NumInteriorRing() , ST_NumInteriorRings() |
Return number of interior rings in Polygon |
ST_NumPoints() |
Return number of points in LineString |
ST_Overlaps() |
Whether one geometry overlaps another |
ST_PointFromGeoHash() |
Convert geohash value to POINT value |
ST_PointFromText() |
Construct Point from WKT |
ST_PointFromWKB() |
Construct Point from WKB |
ST_PointN() |
Return N-th point from LineString |
ST_PolyFromText() , ST_PolygonFromText() |
Construct Polygon from WKT |
ST_PolyFromWKB() , ST_PolygonFromWKB() |
Construct Polygon from WKB |
ST_Simplify() |
Return simplified geometry |
ST_SRID() |
Return spatial reference system ID for geometry |
ST_StartPoint() |
Start Point of LineString |
ST_SymDifference() |
Return point set symmetric difference of two geometries |
ST_Touches() |
Whether one geometry touches another |
ST_Union() |
Return point set union of two geometries |
ST_Validate() |
Return validated geometry |
ST_Within() |
Whether one geometry is within another |
ST_X() |
Return X coordinate of Point |
ST_Y() |
Return Y coordinate of Point |
StartPoint() (deprecated) |
Start Point of LineString |
Touches() (deprecated) |
Whether one geometry touches another |
Within() (deprecated) |
Whether MBR of one geometry is within MBR of another |
X() (deprecated) |
Return X coordinate of Point |
Y() (deprecated) |
Return Y coordinate of Point |
Spatial values, or geometries, have the properties described at Section 11.4.2.2, “Geometry Class”. The following discussion lists general spatial function argument-handling characteristics. Specific functions or groups of functions may have additional argument-handling characteristics, as discussed in the sections where those function descriptions occur.
Spatial functions are defined only for valid geometry values.
The spatial reference identifier (SRID) of a geometry identifies the coordinate space in which the geometry is defined. In MySQL, the SRID value is an integer associated with the geometry value. The maximum usable SRID value is 232−1. If a larger value is given, only the lower 32 bits are used.
In MySQL, all computations are done assuming SRID 0, regardless of the actual SRID value. SRID 0 represents an infinite flat Cartesian plane with no units assigned to its axes. In the future, computations may use the specified SRID values. To ensure SRID 0 behavior, create geometry values using SRID 0. SRID 0 is the default for new geometry values if no SRID is specified.
Geometry values produced by any spatial function inherit the SRID of the geometry arguments.
Spatial functions that take multiple geometry arguments require
those arguments to have the same SRID value (that is, same value
in the lower 32 bits). Assuming equal SRIDs, spatial functions do
nothing with them after performing the equality check; geometry
values are implicitly handled using Cartesian coordinates (SRID
0). If a spatial function returns
ER_GIS_DIFFERENT_SRIDS
, it means
that the geometry arguments did not all have the same SRID. You
must modify them to have the same SRID.
The Open Geospatial Consortium guidelines require that input polygons already be closed, so unclosed polygons are rejected as invalid rather than being closed.
Empty geometry-collection handling is as follows: An empty WKT
input geometry collection may be specified as
'GEOMETRYCOLLECTION()'
. This is also the output
WKT resulting from a spatial operation that produces an empty
geometry collection.
During parsing of a nested geometry collection, the collection is flattened and its basic components are used in various GIS operations to compute results. This provides additional flexibility to users because it is unnecessary to be concerned about the uniqueness of geometry data. Nested geometry collections may be produced from nested GIS function calls without having to be explicitly flattened first.
These functions take as arguments a Well-Known Text (WKT) representation and, optionally, a spatial reference system identifier (SRID). They return the corresponding geometry.
ST_GeomFromText()
accepts a WKT
value of any geometry type as its first argument. Other functions
provide type-specific construction functions for construction of
geometry values of each geometry type.
For a description of WKT format, see Well-Known Text (WKT) Format.
GeomCollFromText(
,
wkt
[,
srid
])GeometryCollectionFromText(
wkt
[,
srid
])
ST_GeomCollFromText()
,
ST_GeometryCollectionFromText()
,
ST_GeomCollFromTxt()
,
GeomCollFromText()
, and
GeometryCollectionFromText()
are synonyms. For more information, see the description of
ST_GeomCollFromText()
.
GeomCollFromText()
and
GeometryCollectionFromText()
are deprecated as of MySQL 5.7.6 and will be removed in a
future MySQL release. Use
ST_GeomCollFromText()
and
ST_GeometryCollectionFromText()
instead.
GeomFromText(
,
wkt
[,
srid
])GeometryFromText(
wkt
[,
srid
])
ST_GeomFromText()
,
ST_GeometryFromText()
,
GeomFromText()
, and
GeometryFromText()
are synonyms. For more information, see the description of
ST_GeomFromText()
.
GeomFromText()
and
GeometryFromText()
are deprecated as of MySQL 5.7.6 and will be removed in a
future MySQL release. Use
ST_GeomFromText()
and
ST_GeometryFromText()
instead.
LineFromText(
,
wkt
[,
srid
])LineStringFromText(
wkt
[,
srid
])
ST_LineFromText()
,
ST_LineStringFromText()
,
LineFromText()
, and
LineStringFromText()
are synonyms. For more information, see the description of
ST_LineFromText()
.
LineFromText()
and
LineStringFromText()
are deprecated as of MySQL 5.7.6 and will be removed in a
future MySQL release. Use
ST_LineFromText()
and
ST_LineStringFromText()
instead.
MLineFromText(
,
wkt
[,
srid
])MultiLineStringFromText(
wkt
[,
srid
])
ST_MLineFromText()
,
ST_MultiLineStringFromText()
,
MLineFromText()
, and
MultiLineStringFromText()
are synonyms. For more information, see the description of
ST_MLineFromText()
.
MLineFromText()
and
MultiLineStringFromText()
are deprecated as of MySQL 5.7.6 and will be removed in a
future MySQL release. Use
ST_MLineFromText()
and
ST_MultiLineStringFromText()
instead.
MPointFromText(
,
wkt
[,
srid
])MultiPointFromText(
wkt
[,
srid
])
ST_MPointFromText()
,
ST_MultiPointFromText()
,
MPointFromText()
, and
MultiPointFromText()
are synonyms. For more information, see the description of
ST_MPointFromText()
.
MPointFromText()
and
MultiPointFromText()
are deprecated as of MySQL 5.7.6 and will be removed in a
future MySQL release. Use
ST_MPointFromText()
and
ST_MultiPointFromText()
instead.
MPolyFromText(
,
wkt
[,
srid
])MultiPolygonFromText(
wkt
[,
srid
])
ST_MPolyFromText()
,
ST_MultiPolygonFromText()
,
MPolyFromText()
, and
MultiPolygonFromText()
are synonyms. For more information, see the description of
ST_MPolyFromText()
.
MPolyFromText()
and
MultiPolygonFromText()
are deprecated as of MySQL 5.7.6 and will be removed in a
future MySQL release. Use
ST_MPolyFromText()
and
ST_MultiPolygonFromText()
instead.
ST_PointFromText()
and
PointFromText()
are synonyms.
For more information, see the description of
ST_PointFromText()
.
PointFromText()
is deprecated
as of MySQL 5.7.6 and will be removed in a future MySQL
release. Use ST_PointFromText()
instead.
PolyFromText(
,
wkt
[,
srid
])PolygonFromText(
wkt
[,
srid
])
ST_PolyFromText()
,
ST_PolygonFromText()
,
PolyFromText()
, and
PolygonFromText()
are synonyms. For more information, see the description of
ST_PolyFromText()
.
PolyFromText()
and
PolygonFromText()
are deprecated as of MySQL 5.7.6 and will be removed in a
future MySQL release. Use
ST_PolyFromText()
and
ST_PolygonFromText()
instead.
ST_GeomCollFromText(
,
wkt
[,
srid
])ST_GeometryCollectionFromText(
,
wkt
[,
srid
])ST_GeomCollFromTxt(
wkt
[,
srid
])
Constructs a GeometryCollection
value using
its WKT representation and SRID.
If the geometry argument is NULL
or not a
syntactically well-formed geometry, or if the SRID argument is
NULL
, the return value is
NULL
.
mysql>SET @g = "MULTILINESTRING((10 10, 11 11), (9 9, 10 10))";
mysql>SELECT ST_AsText(ST_GeomCollFromText(@g));
+--------------------------------------------+ | ST_AsText(ST_GeomCollFromText(@g)) | +--------------------------------------------+ | MULTILINESTRING((10 10,11 11),(9 9,10 10)) | +--------------------------------------------+
ST_GeomCollFromText()
,
ST_GeometryCollectionFromText()
,
ST_GeomCollFromTxt()
,
GeomCollFromText()
, and
GeometryCollectionFromText()
are synonyms.
ST_GeomCollFromTxt()
was added in MySQL 5.7.6.
ST_GeomFromText(
,
wkt
[,
srid
])ST_GeometryFromText(
wkt
[,
srid
])
Constructs a geometry value of any type using its WKT representation and SRID.
If the geometry argument is NULL
or not a
syntactically well-formed geometry, or if the SRID argument is
NULL
, the return value is
NULL
.
ST_GeomFromText()
,
ST_GeometryFromText()
,
GeomFromText()
, and
GeometryFromText()
are synonyms.
ST_LineFromText(
,
wkt
[,
srid
])ST_LineStringFromText(
wkt
[,
srid
])
Constructs a LineString
value using its WKT
representation and SRID.
If the geometry argument is NULL
or not a
syntactically well-formed geometry, or if the SRID argument is
NULL
, the return value is
NULL
.
ST_LineFromText()
,
ST_LineStringFromText()
,
LineFromText()
, and
LineStringFromText()
are synonyms.
ST_MLineFromText(
,
wkt
[,
srid
])ST_MultiLineStringFromText(
wkt
[,
srid
])
Constructs a MultiLineString
value using
its WKT representation and SRID.
If the geometry argument is NULL
or not a
syntactically well-formed geometry, or if the SRID argument is
NULL
, the return value is
NULL
.
ST_MLineFromText()
,
ST_MultiLineStringFromText()
,
MLineFromText()
, and
MultiLineStringFromText()
are synonyms.
ST_MLineFromText()
and
ST_MultiLineStringFromText()
were added in MySQL 5.7.6.
ST_MPointFromText(
,
wkt
[,
srid
])ST_MultiPointFromText(
wkt
[,
srid
])
Constructs a MultiPoint
value using its WKT
representation and SRID.
If the geometry argument is NULL
or not a
syntactically well-formed geometry, or if the SRID argument is
NULL
, the return value is
NULL
.
As of MySQL 5.7.9, spatial functions such as
ST_MPointFromText()
and
ST_GeomFromText()
that accept
WKT-format representations of MultiPoint
values permit individual points within values to be surrounded
by parentheses. For example, both of the following function
calls are valid, whereas before MySQL 5.7.9 the second one
produces an error:
ST_MPointFromText('MULTIPOINT (1 1, 2 2, 3 3)') ST_MPointFromText('MULTIPOINT ((1 1), (2 2), (3 3))')
ST_MPointFromText()
,
ST_MultiPointFromText()
,
MPointFromText()
, and
MultiPointFromText()
are synonyms.
ST_MPointFromText()
and
ST_MultiPointFromText()
were added in MySQL 5.7.6.