Table of Contents
GROUP BY
Clauses
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 allowed for writing expressions in MySQL. Instructions for
writing stored functions and user-defined functions are given in
Chapter 18, Stored Procedures and Functions, and
Section 26.2, “Adding New Functions to MySQL”. See
Section 8.2.3, “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 5.1.6, “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
This table is part of an ongoing process to expand and simplify the information provided on these elements. Further improvements to the table, and corresponding descriptions will be applied over the coming months.
Name | Description |
---|---|
ABS() | Return the absolute value |
ACOS() | Return the arc cosine |
ADDDATE() (v4.1.1) | Add dates |
ADDTIME() (v4.1.1) | Add time |
AES_DECRYPT() | Decrypt using AES |
AES_ENCRYPT() | Encrypt using AES |
AND , && | Logical AND |
ASCII() | Return numeric value of left-most character |
ASIN() | Return the arc sine |
ATAN2() , ATAN() | Return the arc tangent of the two arguments |
ATAN() | Return the arc tangent |
AVG() | Return the average value of the argument |
BENCHMARK() | Repeatedly execute an expression |
BETWEEN ... AND ... | Check whether a value is within a range of values |
BIN() | Return a string representation of the argument |
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() (v4.1.1) | Return bitwise xor |
& | Bitwise AND |
~ | Invert bits |
| | Bitwise OR |
^ | Bitwise XOR |
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 |
CHAR_LENGTH() | Return number of characters in argument |
CHAR() | Return the character for each integer passed |
CHARACTER_LENGTH() | A synonym for CHAR_LENGTH() |
CHARSET() (v4.1.0) | Return the character set of the argument |
COALESCE() | Return the first non-NULL argument |
COERCIBILITY() (v4.1.1) | Return the collation coercibility value of the string argument |
COLLATION() (v4.1.0) | Return the collation of the string argument |
COMPRESS() (v4.1.1) | Return result as a binary string |
CONCAT_WS() | Return concatenate with separator |
CONCAT() | Return concatenated string |
CONNECTION_ID() | Return the connection ID (thread ID) for the connection |
CONV() | Convert numbers between different number bases |
CONVERT_TZ() (v4.1.3) | Convert from one timezone to another |
Convert() | Cast a value as a certain type |
COS() | Return the cosine |
COT() | Return the cotangent |
COUNT(DISTINCT) | Return the count of a number of different values |
COUNT() | Return a count of the number of rows returned |
CRC32() (v4.1.0) | Compute a cyclic redundancy check value |
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 | Return the username and hostname combination |
CURTIME() | Return the current time |
DATABASE() | Return the default (current) database name |
DATE_ADD() | Add two dates |
DATE_FORMAT() | Format date as specified |
DATE_SUB() | Subtract two dates |
DATE() (v4.1.1) | Extract the date part of a date or datetime expression |
DATEDIFF() (v4.1.1) | Subtract two dates |
DAY() (v4.1.1) | Synonym for DAYOFMONTH() |
DAYNAME() (v4.1.21) | Return the name of the weekday |
DAYOFMONTH() | Return the day of the month (1-31) |
DAYOFWEEK() | Return the weekday index of the argument |
DAYOFYEAR() | Return the day of the year (1-366) |
DECODE() | Decodes a string encrypted using ENCODE() |
DEFAULT() | Return the default value for a table column |
DEGREES() | Convert radians to degrees |
DES_DECRYPT() | Decrypt a string |
DES_ENCRYPT() | Encrypt a string |
DIV (v4.1.0) | Integer division |
/ | Division operator |
ELT() | Return string at index number |
ENCODE() | Encode a string |
ENCRYPT() | Encrypt a string |
<=> | NULL-safe equal to operator |
= | Equal operator |
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 |
EXTRACT | Extract part of a date |
FIELD() | Return the index (position) of the first argument in the subsequent arguments |
FIND_IN_SET() | Return the index position of the first argument within the 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_DAYS() | Convert a day number to a date |
FROM_UNIXTIME() | Format date as a UNIX timestamp |
GET_FORMAT() (v4.1.1) | Return a date format string |
GET_LOCK() | Get a named lock |
>= | Greater than or equal operator |
> | Greater than operator |
GREATEST() | Return the largest argument |
GROUP_CONCAT() (v4.1) | Return a concatenated string |
HEX() | Return a hexadecimal representation of a decimal or string value |
HOUR() | Extract the hour |
IF() | If/else construct |
IFNULL() | Null if/else construct |
IN() | Check 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 |
INSERT() | Insert a substring at the specified position up to the specified number of characters |
INSTR() | Return the index of the first occurrence of substring |
INTERVAL() | Return the index of the argument that is less than the first argument |
IS_FREE_LOCK() | Checks whether the named lock is free |
IS NOT NULL | NOT NULL value test |
IS NOT | Test a value against a boolean |
IS NULL | NULL value test |
IS_USED_LOCK() (v4.1.0) | Checks whether the named lock is in use. Return connection identifier if true. |
IS | Test a value against a boolean |
ISNULL() | Test whether the argument is NULL |
LAST_DAY (v4.1.1) | 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 shift |
LEFT() | Return the leftmost number of characters as specified |
LENGTH() | Return the length of a string in bytes |
<= | Less than or equal operator |
< | Less than operator |
LIKE | Simple pattern matching |
LN() | Return the natural logarithm of the argument |
LOAD_FILE() | Load the named file |
LOCALTIME() , LOCALTIME | Synonym for NOW() |
LOCALTIMESTAMP , LOCALTIMESTAMP() (v4.0.6) | Synonym for NOW() |
LOCATE() | Return the position of the first occurrence of substring |
LOG10() | Return the base-10 logarithm of the argument |
LOG2() | Return the base-2 logarithm of the argument |
LOG() | Return the natural logarithm of the first 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() (v4.1.1) | Create a date from the year and day of year |
MAKETIME (v4.1.1) | MAKETIME() |
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 |
MD5() | Calculate MD5 checksum |
MICROSECOND() (v4.1.1) | Return the microseconds from argument |
MID() | Return a substring starting from the specified position |
MIN() | Return the minimum value |
- | Minus operator |
MINUTE() | Return the minute from the argument |
MOD() | Return the remainder |
% | Modulo operator |
MONTH() | Return the month from the date passed |
MONTHNAME() (v4.1.21) | Return the name of the month |
NAME_CONST() (v5.0.12) | Causes the column to have the given name |
NOT BETWEEN ... AND ... | Check whether a value is not within a range of values |
!= , <> | Not equal operator |
NOT IN() | Check whether a value is not within a set of values |
NOT LIKE | Negation of simple pattern matching |
NOT REGEXP | Negation of REGEXP |
NOT , ! | Negates value |
NOW() | Return the current date and time |
NULLIF() | Return NULL if expr1 = expr2 |
OCT() | Return an octal representation of a decimal number |
OCTET_LENGTH() | A synonym for LENGTH() |
OLD_PASSWORD() (v4.1) | Return the value of the old (pre-4.1) implementation of PASSWORD |
|| , OR | Logical OR |
ORD() | Return character code for leftmost character of the argument |
PASSWORD() | 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 |
+ | Addition operator |
POSITION() | A synonym for LOCATE() |
POW() | Return the argument raised to the specified power |
POWER() | Return the argument raised to the specified power |
PROCEDURE ANALYSE() | 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 |
REGEXP | Pattern matching using regular expressions |
RELEASE_LOCK() | Releases 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 shift |
RIGHT() | Return the specified rightmost number of characters |
RLIKE | Synonym for REGEXP |
ROUND() | Round the argument |
ROW_COUNT() (v5.0.1) | The number of rows updated |
RPAD() | Append string the specified number of times |
RTRIM() | Remove trailing spaces |
SCHEMA() (v5.0.2) | A 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 |
SIGN() | Return the sign of the argument |
SIN() | Return the sine of the argument |
SLEEP() (v5.0.12) | Sleep for a number of seconds |
SOUNDEX() | Return a soundex string |
SOUNDS LIKE (v4.1.0) | Compare sounds |
SPACE() | Return a string of the specified number of spaces |
SQRT() | Return the square root of the argument |
STD() | Return the population standard deviation |
STDDEV_POP() (v5.0.3) | Return the population standard deviation |
STDDEV_SAMP() (v5.0.3) | Return the sample standard deviation |
STDDEV() | Return the population standard deviation |
STR_TO_DATE() (v4.1.1) | Convert a string to a date |
STRCMP() | Compare two strings |
SUBDATE() | When invoked with three arguments a synonym for DATE_SUB() |
SUBSTR() | Return the substring as specified |
SUBSTRING_INDEX() | Return a substring from a string before the specified number of occurrences of the delimiter |
SUBSTRING() | Return the substring as specified |
SUBTIME() (v4.1.1) | 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_FORMAT() | Format as time |
TIME_TO_SEC() | Return the argument converted to seconds |
TIME() (v4.1.1) | Extract the time portion of the expression passed |
TIMEDIFF() (v4.1.1) | Subtract time |
* | Times operator |
TIMESTAMP() (v4.1.1) | With a single argument, this function returns the date or datetime expression. With two arguments, the sum of the arguments |
TIMESTAMPADD() (v5.0.0) | Add an interval to a datetime expression |
TIMESTAMPDIFF() (v5.0.0) | Subtract an interval from a datetime expression |
TO_DAYS() | Return the date argument converted to days |
TRIM() | Remove leading and trailing spaces |
TRUNCATE() | Truncate to specified number of decimal places |
UCASE() | Synonym for UPPER() |
- | Change the sign of the argument |
UNCOMPRESS() (v4.1.1) | Uncompress a string compressed |
UNCOMPRESSED_LENGTH() (v4.1.1) | Return the length of a string before compression |
UNHEX() (v4.1.2) | Convert each pair of hexadecimal digits to a character |
UNIX_TIMESTAMP() | Return a UNIX timestamp |
UPPER() | Convert to uppercase |
USER() | Return the current username and hostname |
UTC_DATE() (v4.1.1) | Return the current UTC date |
UTC_TIME() (v4.1.1) | Return the current UTC time |
UTC_TIMESTAMP() (v4.1.1) | Return the current UTC date and time |
UUID() (v4.1.2) | Return a Universal Unique Identifier (UUID) |
VALUES() (v4.1.1) | Defines the values to be used during an INSERT |
VAR_POP() (v5.0.3) | Return the population standard variance |
VAR_SAMP() (v5.0.3) | Return the sample variance |
VARIANCE() (v4.1) | Return the population standard variance |
VERSION() | Returns a string that indicates the MySQL server version |
WEEK() | Return the week number |
WEEKDAY() | Return the weekday index |
WEEKOFYEAR() (v4.1.1) | Return the calendar week of the date (1-53) |
XOR | Logical XOR |
YEAR() | Return the year |
YEARWEEK() | Return the year and week |
Name | Description |
---|---|
AND , && | Logical AND |
BETWEEN ... AND ... | Check whether a value is within a range of values |
BINARY | Cast a string to a binary string |
& | Bitwise AND |
~ | Invert bits |
| | Bitwise OR |
^ | Bitwise XOR |
CASE | Case operator |
DIV (v4.1.0) | Integer division |
/ | Division operator |
<=> | NULL-safe equal to operator |
= | Equal operator |
>= | Greater than or equal operator |
> | Greater than operator |
IS NOT NULL | NOT NULL value test |
IS NOT | Test a value against a boolean |
IS NULL | NULL value test |
IS | Test a value against a boolean |
<< | Left shift |
<= | Less than or equal operator |
< | Less than operator |
LIKE | Simple pattern matching |
- | Minus operator |
% | Modulo operator |
NOT BETWEEN ... AND ... | Check whether a value is not within a range of values |
!= , <> | Not equal operator |
NOT LIKE | Negation of simple pattern matching |
NOT REGEXP | Negation of REGEXP |
NOT , ! | Negates value |
|| , OR | Logical OR |
+ | Addition operator |
REGEXP | Pattern matching using regular expressions |
>> | Right shift |
RLIKE | Synonym for REGEXP |
SOUNDS LIKE (v4.1.0) | Compare sounds |
* | Times operator |
- | Change the sign of the argument |
XOR | Logical XOR |
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.
BINARY, COLLATE ! - (unary minus), ~ (unary bit inversion) ^ *, /, DIV, %, MOD -, + <<, >> & | =, <=>, >=, >, <=, <, <>, !=, IS, LIKE, REGEXP, IN BETWEEN, CASE, WHEN, THEN, ELSE NOT &&, AND XOR ||, OR :=
The ||
operator
has a precedence between
^
and
the unary operators if the PIPES_AS_CONCAT
SQL mode is enabled.
The precedence shown for NOT
is as of MySQL 5.0.2. For earlier versions, or from 5.0.2 on if
the HIGH_NOT_PRECEDENCE
SQL mode is enabled,
the precedence of NOT
is the
same as that of the
!
operator.
See Section 5.1.6, “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
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 numbers to strings as necessary, and vice versa.
mysql>SELECT 1+'1';
-> 2 mysql>SELECT CONCAT(2,' test');
-> '2 test'
It is also possible to perform explicit conversions. If you want
to convert a number to a string explicitly, use the
CAST()
or
CONCAT()
function
(CAST()
is preferable):
mysql>SELECT 38.8, CAST(38.8 AS CHAR);
-> 38.8, '38.8' mysql>SELECT 38.8, CONCAT(38.8);
-> 38.8, '38.8'
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.
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. Note that this is not done for the arguments
to IN()
! To be safe, always
use complete datetime, date, or time strings when doing
comparisons.
In all other cases, the arguments are compared as floating-point (real) numbers.
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
Note that when you are comparing 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 will not be 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.1.5.8, “Problems with Floating-Point Comparisons”.
Name | Description |
---|---|
BETWEEN ... AND ... | Check whether a value is within a range of values |
COALESCE() | Return the first non-NULL argument |
<=> | NULL-safe equal to operator |
= | Equal operator |
>= | Greater than or equal operator |
> | Greater than operator |
GREATEST() | Return the largest argument |
IN() | Check whether a value is within a set of values |
INTERVAL() | Return the index of the argument that is less than the first argument |
IS NOT NULL | NOT NULL value test |
IS NOT | Test a value against a boolean |
IS NULL | NULL value test |
IS | Test a value against a boolean |
ISNULL() | Test whether the argument is NULL |
LEAST() | Return the smallest argument |
<= | Less than or equal operator |
< | Less than operator |
LIKE | Simple pattern matching |
NOT BETWEEN ... AND ... | Check whether a value is not within a range of values |
!= , <> | Not equal operator |
NOT IN() | Check whether a value is not within a set of values |
NOT LIKE | Negation of simple pattern matching |
SOUNDS LIKE (v4.1.0) | Compare sounds |
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.
Some of the functions in this section (such as
LEAST()
and
GREATEST()
) return values other
than 1
(TRUE
),
0
(FALSE
), or
NULL
. However, the value they return is based
on comparison operations performed according to the rules
described in Section 11.2.2, “Type Conversion in Expression Evaluation”.
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 11.9, “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
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
.
mysql>SELECT 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
-> 1, 1, 0 mysql>SELECT 1 = 1, NULL = NULL, 1 = NULL;
-> 1, NULL, NULL
Not equal:
mysql>SELECT '.01' <> '0.01';
-> 1 mysql>SELECT .01 <> '0.01';
-> 0 mysql>SELECT 'zapp' <> 'zappp';
-> 1
Less than or equal:
mysql> SELECT 0.1 <= 2;
-> 1
Less than:
mysql> SELECT 2 < 2;
-> 0
Greater than or equal:
mysql> SELECT 2 >= 2;
-> 1
Greater than:
mysql> SELECT 2 > 2;
-> 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
-> 1, 1, 0
IS
syntax
was added in MySQL 5.0.2.
boolean_value
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
IS NOT
syntax
was added in MySQL 5.0.2.
boolean_value
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
:
You can find the row that contains the most recent
AUTO_INCREMENT
value by issuing a
statement of the following form immediately after
generating the value:
SELECT * FROMtbl_name
WHEREauto_col
IS NULL
This behavior can be disabled by setting
SQL_AUTO_IS_NULL=0
. See
Section 12.5.3, “SET
Syntax”.
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.
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 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 11.2.2, “Type Conversion in Expression Evaluation”, but applied to all the
three arguments.
min
<=
expr
AND
expr
<=
max
)
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, you should 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.
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'
Before MySQL 5.0.13,
GREATEST()
returns
NULL
only if all arguments are
NULL
. As of 5.0.13, it returns
NULL
if any argument is
NULL
.
Returns 1
if
expr
is equal to any of the
values in the IN
list, else returns
0
. If all values are constants, they are
evaluated according to the type of
expr
and sorted. The search for
the item then is done using a binary search. This means
IN
is very quick if the
IN
value list consists entirely of
constants. Otherwise, type conversion takes place according
to the rules described in Section 11.2.2, “Type Conversion in Expression Evaluation”,
but applied to all the arguments.
mysql>SELECT 2 IN (0,3,5,7);
-> 0 mysql>SELECT 'wefwf' IN ('wee','wefwf','weg');
-> 1
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');
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 12.2.8.3, “Subqueries with ANY
, IN
, and
SOME
”.
This is the same as NOT
(
.
expr
IN
(value
,...))
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 false.)
The ISNULL()
function shares
some special behaviors with the
IS
NULL
comparison operator. See the description of
IS
NULL
.
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
With two or more arguments, returns the smallest (minimum-valued) argument. The arguments are compared using the following rules:
If the return value is used in an
INTEGER
context or all arguments are
integer-valued, they are compared as integers.
If the return value is used in a REAL
context or all arguments are real-valued, they are
compared as reals.
If any argument is a case-sensitive string, the arguments are compared as case-sensitive strings.
In all other cases, the arguments are compared as case-insensitive strings.
Before MySQL 5.0.13, LEAST()
returns NULL
only if all arguments are
NULL
. As of 5.0.13, it returns
NULL
if any argument is
NULL
.
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'
Note that the preceding conversion rules can produce strange results in some borderline cases:
mysql> SELECT CAST(LEAST(3600, 9223372036854775808.0) as SIGNED);
-> -9223372036854775808
This happens because MySQL reads
9223372036854775808.0
in an integer
context. The integer representation is not good enough to
hold the value, so it wraps to a signed integer.
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 non-zero value for
TRUE
.
Note that MySQL evaluates any non-zero or
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 non-zero, 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
.
Note that the precedence of the
NOT
operator changed in
MySQL 5.0.2. See Section 11.2.1, “Operator Precedence”.
Logical AND. Evaluates to 1
if all
operands are non-zero and not NULL
, to
0
if one or more operands are
0
, otherwise NULL
is
returned.
mysql>SELECT 1 && 1;
-> 1 mysql>SELECT 1 && 0;
-> 0 mysql>SELECT 1 && NULL;
-> NULL mysql>SELECT 0 && NULL;
-> 0 mysql>SELECT NULL && 0;
-> 0
Logical OR. When both operands are
non-NULL
, the result is
1
if any operand is non-zero, and
0
otherwise. With a
NULL
operand, the result is
1
if the other operand is non-zero, and
NULL
otherwise. If both operands are
NULL
, the result is
NULL
.
mysql>SELECT 1 || 1;
-> 1 mysql>SELECT 1 || 0;
-> 1 mysql>SELECT 0 || 0;
-> 0 mysql>SELECT 0 || NULL;
-> NULL mysql>SELECT 1 || NULL;
-> 1
Logical XOR. Returns NULL
if either
operand is NULL
. For
non-NULL
operands, evaluates to
1
if an odd number of operands is
non-zero, 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)
.
Name | Description |
---|---|
CASE | Case operator |
IF() | If/else construct |
IFNULL() | Null if/else construct |
NULLIF() | Return NULL if expr1 = expr2 |
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 version returns the
result
where
.
The second version returns the result for the first condition
that is true. If there was no matching result value, the
result after value
=compare_value
ELSE
is returned, or
NULL
if there is no ELSE
part.
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
The default return type of a
CASE
expression is the
compatible aggregated type of all return values, but also
depends on the context in which it is used. If used in a
string context, the result is returned as a string. If used in
a numeric context, then the result is returned as a decimal,
real, or integer value.
The syntax of the CASE
expression shown here differs slightly
from that of the SQL CASE
statement described in
Section 18.2.10.2, “CASE
Statement”, for use inside stored
routines. The CASE
statement cannot have
an ELSE NULL
clause, and it is terminated
with END CASE
instead of
END
.
If expr1
is TRUE
(
and expr1
<>
0
) then
expr1
<> NULLIF()
returns
expr2
; otherwise it returns
expr3
.
IF()
returns a numeric or
string value, depending on the context in which it is used.
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 only one of expr2
or
expr3
is explicitly
NULL
, the result type of the
IF()
function is the type of
the non-NULL
expression.
expr1
is evaluated as an integer
value, which means that if you are testing floating-point or
string values, you should do so using a comparison operation.
mysql>SELECT IF(0.1,1,0);
-> 0 mysql>SELECT IF(0.1<>0,1,0);
-> 1
In the first case shown,
IF(0.1)
returns
0
because 0.1
is
converted to an integer value, resulting in a test of
IF(0)
. This may not be what
you expect. In the second case, the comparison tests the
original floating-point value to see whether it is non-zero.
The result of the comparison is used as an integer.
The default return type of
IF()
(which may matter when it
is stored into a temporary table) is calculated as follows:
Expression | Return Value |
expr2 or expr3
returns a string | string |
expr2 or expr3
returns a floating-point value | floating-point |
expr2 or expr3
returns an integer | integer |
If expr2
and
expr3
are both strings, the result
is case sensitive if either string is case sensitive.
There is also an IF
statement, which differs from the
IF()
function described here. See
Section 18.2.10.1, “IF
Statement”.
If expr1
is not
NULL
,
IFNULL()
returns
expr1
; otherwise it returns
expr2
.
IFNULL()
returns a numeric or
string value, depending on the context in which it is used.
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 result value 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 | char(4) | | | | | +-------+---------+------+-----+---------+-------+
In this example, the type of the test
column is CHAR(4)
.
Returns NULL
if
is true, otherwise
returns expr1
=
expr2
expr1
. This is the same as
CASE WHEN
.
expr1
=
expr2
THEN NULL ELSE
expr1
END
mysql>SELECT NULLIF(1,1);
-> NULL mysql>SELECT NULLIF(1,2);
-> 1
Note that MySQL evaluates expr1
twice if the arguments are not equal.
Name | Description |
---|---|
ASCII() | Return numeric value of left-most character |
BIN() | Return a string representation of the argument |
BIT_LENGTH() | Return length of argument in bits |
CHAR_LENGTH() | Return number of characters in argument |
CHAR() | Return the character for each integer passed |
CHARACTER_LENGTH() | A synonym for CHAR_LENGTH() |
CONCAT_WS() | Return concatenate with separator |
CONCAT() | Return concatenated string |
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() | Return the index (position) of the first argument in the subsequent arguments |
FIND_IN_SET() | Return the index position of the first argument within the second argument |
FORMAT() | Return a number formatted to specified number of decimal places |
HEX() | Return a hexadecimal representation of a decimal or string value |
INSERT() | Insert a substring at the specified position up to the 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 |
OCTET_LENGTH() | A synonym for LENGTH() |
ORD() | Return character code for leftmost character of the argument |
POSITION() | A synonym for LOCATE() |
QUOTE() | Escape the argument for use in an SQL statement |
REGEXP | Pattern matching using regular expressions |
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 | Synonym for REGEXP |
RPAD() | Append string the specified number of times |
RTRIM() | Remove trailing spaces |
SOUNDEX() | Return a soundex string |
SOUNDS LIKE (v4.1.0) | Compare sounds |
SPACE() | Return a string of the specified number of spaces |
STRCMP() | Compare two strings |
SUBSTR() | Return the substring as specified |
SUBSTRING_INDEX() | Return a substring from a string before the specified number of occurrences of the delimiter |
SUBSTRING() | Return the substring as specified |
TRIM() | Remove leading and trailing spaces |
UCASE() | Synonym for UPPER() |
UNHEX() (v4.1.2) | Convert each pair of hexadecimal digits to a character |
UPPER() | Convert to uppercase |
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 7.5.2, “Tuning Server Parameters”.
For functions that operate on string positions, the first position is numbered 1.
For functions that take length arguments, non-integer 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'
As of MySQL 5.0.15, 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(0x65)), CHARSET(CHAR(0x65 USING utf8));
+---------------------+--------------------------------+
| CHARSET(CHAR(0x65)) | CHARSET(CHAR(0x65 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
.
Before MySQL 5.0.15, CHAR()
returns a string in the connection character set and the
USING
clause is unavailable. In addition,
each argument is interpreted modulo 256, so
CHAR(256)
and
CHAR(256*256)
both are
equivalent to CHAR(0)
.
Returns the length of the string
str
, measured in characters. A
multi-byte character counts as a single character. This means
that for a string containing five two-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 non-binary strings, the result is a non-binary string. If the arguments include any binary strings, the result is a binary string. A numeric argument is converted to its equivalent binary string form; if you want to avoid that, you can use an explicit type cast, as in this example:
SELECT CONCAT(CAST(int_col
AS CHAR),char_col
);
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'
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.
Returns 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, 'ej', 'Heja', 'hej', 'foo');
-> 'ej' mysql>SELECT ELT(4, 'ej', 'Heja', 'hej', 'foo');
-> 'foo'
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
(defaults to 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('ej', 'Hej', 'ej', 'Heja', 'hej', 'foo');
-> 2 mysql>SELECT FIELD('fo', 'Hej', 'ej', 'Heja', 'hej', 'foo');
-> 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.
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'
If N_or_S
is a number, returns a
string representation of the hexadecimal value of
N
, where
N
is a longlong
(BIGINT
) number. This is equivalent to
CONV(
.
N
,10,16)
If N_or_S
is a string, returns a
hexadecimal string representation of
N_or_S
where each character in
N_or_S
is converted to two
hexadecimal digits. The inverse of this operation is performed
by the UNHEX()
function.
mysql>SELECT HEX(255);
-> 'FF' mysql>SELECT 0x616263;
-> 'abc' mysql>SELECT HEX('abc');
-> 616263
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 multi-byte 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 multi-byte safe, and is case sensitive only if at least one argument is a binary string.
Returns the leftmost len
characters
from the string str
, or
NULL
if any argument is
NULL
.
mysql> SELECT LEFT('foobarbar', 5);
-> 'fooba'
Returns the length of the string
str
, measured in bytes. A
multi-byte character counts as multiple bytes. This means that
for a string containing five two-byte characters,
LENGTH()
returns
10
, whereas
CHAR_LENGTH()
returns
5
.
mysql> SELECT LENGTH('text');
-> 4
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 pathname 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 file does not exist or cannot be read because one of
the preceding conditions is not satisfied, the function
returns NULL
.
As of MySQL 5.0.19, the
character_set_filesystem
system variable
controls interpretation of filenames 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
.
mysql>SELECT LOCATE('bar', 'foobarbar');
-> 4 mysql>SELECT LOCATE('xbar', 'foobar');
-> 0 mysql>SELECT LOCATE('bar', 'foobarbar', 5);
-> 7
This function is multi-byte 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'
This function is multi-byte safe.
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 multi-byte 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 multi-byte 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 × 2562) ...
If the leftmost character is not a multi-byte 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 quotes and with each instance of
single quote (“'
”), backslash
(“\
”), ASCII
NUL
, and Control-Z preceded by a backslash.
If the argument is NULL
, the return value
is the word “NULL” without enclosing single
quotes.
mysql>SELECT QUOTE('Don\'t!');
-> 'Don\'t!' mysql>SELECT QUOTE(NULL);
-> NULL
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 multi-byte safe.
Returns the string str
with the
order of the characters reversed.
mysql> SELECT REVERSE('abc');
-> 'cba'
This function is multi-byte 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 multi-byte 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 multi-byte safe.
Returns the string str
with
trailing space characters removed.
mysql> SELECT RTRIM('barbar ');
-> 'barbar'
This function is multi-byte 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 non-alphabetic 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 multi-byte character sets,
including utf-8
.
We hope to remove these limitations in a future release. 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.
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 multi-byte 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 multi-byte safe.
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 multi-byte safe.
Performs the inverse operation of
HEX(
.
That is, it interprets each pair of hexadecimal digits in the
argument as a number and converts it to the character
represented by the number. The resulting characters are
returned as a binary string.
str
)
mysql>SELECT UNHEX('4D7953514C');
-> 'MySQL' mysql>SELECT 0x4D7953514C;
-> '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
UNHEX()
encounters any
non-hexadecimal digits in the argument, it returns
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 'aa'
is stored
into a CHAR(3)
column as
'aa '
and retrieved as
'aa'
(with the trailing pad space
stripped), so UNHEX()
for the
column value returns 'A'
. By contrast
'aa'
is stored into a
BINARY(3)
column as
'aa\0'
and retrieved as
'aa\0'
(with the trailing pad
0x00
byte not stripped).
'\0'
is not a legal hexadecimal digit, so
UNHEX()
for the column value
returns NULL
.
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'
This function is multi-byte safe.
Name | Description |
---|---|
LIKE | Simple pattern matching |
NOT LIKE | Negation of simple pattern matching |
SOUNDS LIKE (v4.1.0) | Compare sounds |
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 SQL simple regular expression
comparison. 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 | +--------------------------------------+
With LIKE
you can use the
following two wildcard characters in the pattern:
Character | Description |
% | 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.
String | Description |
\% | 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.
As of MySQL 5.0.16, 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 a binary string:
mysql>SELECT 'abc' LIKE 'ABC';
-> 1 mysql>SELECT 'abc' LIKE BINARY 'ABC';
-> 0
In MySQL, LIKE
is allowed
on numeric expressions. (This is an extension to the
standard SQL LIKE
.)
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.)
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;
,
expr
NOT REGEXP pat
expr
NOT RLIKE pat
This is the same as NOT
(
.
expr
REGEXP
pat
)
,
expr
REGEXP pat
expr
RLIKE pat
Performs a pattern match of a string expression
expr
against a pattern
pat
. The pattern can be an
extended regular expression. The syntax for regular
expressions is discussed in Section 11.4.2, “Regular Expressions”.
Returns 1
if
expr
matches
pat
; otherwise it returns
0
. If either
expr
or
pat
is NULL
,
the result is NULL
.
RLIKE
is a synonym for REGEXP
,
provided for mSQL
compatibility.
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
strings.
REGEXP
is not case
sensitive, except when used with binary strings.
mysql>SELECT 'Monty!' REGEXP 'm%y%%';
-> 0 mysql>SELECT 'Monty!' REGEXP '.*';
-> 1 mysql>SELECT 'new*\n*line' REGEXP 'new\\*.\\*line';
-> 1 mysql>SELECT 'a' REGEXP 'A', 'a' REGEXP BINARY 'A';
-> 1 0 mysql>SELECT 'a' REGEXP '^[a-d]';
-> 1
REGEXP
and
RLIKE
use the current character set when deciding the type of a
character. The default is latin1
(cp1252
West European).
The REGEXP
and
RLIKE
operators work in byte-wise fashion, so they are not
multi-byte safe and may produce unexpected results with
multi-byte 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.
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()
uses the current
character set when performing comparisons. This makes the
default comparison behavior case insensitive unless one or
both of the operands are binary strings.
Name | Description |
---|---|
NOT REGEXP | Negation of REGEXP |
REGEXP | Pattern matching using regular expressions |
RLIKE | Synonym for REGEXP |
A regular expression is a powerful way of specifying a pattern for a complex search.
MySQL uses Henry Spencer's implementation of regular
expressions, which is aimed at conformance with POSIX 1003.2.
See Appendix G, Credits. MySQL uses the extended version
to support pattern-matching operations performed with the
REGEXP
operator in SQL
statements. See Section 3.3.4.7, “Pattern Matching”, and
Section 11.4.1, “String Comparison Functions”.
This section is a summary, with examples, of the special
characters and constructs that can be used in MySQL for
REGEXP
operations. It 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.
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.
Non-trivial regular expressions use certain special constructs
so that they can match more than one string. For example, the
regular expression hello|word
matches either
the string hello
or the string
word
.
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
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}
{n}
or {m,n}
notation
provides a more general way of writing regular expressions
that match many occurrences of the previous atom (or
“piece”) of the pattern. 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{n}
matches exactly
n
instances of a
.
a{n,}
matches n
or
more instances of a
.
a{m,n}
matches m
through n
instances of
a
, inclusive.
m
and n
must be in the
range from 0
to
RE_DUP_MAX
(default 255), inclusive. If
both m
and n
are
given, m
must be less than or equal to
n
.
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]+$';
-> 0
[.characters.]
Within a bracket expression (written using
[
and ]
), matches the
sequence of characters of that collating element.
characters
is either a single character
or a character name like newline
. The
following table lists the allowable character names.
The following table shows the allowable character names and the characters that they match. For characters given as numeric values, the values are represented in octal.
Name | Character | Name | Character |
NUL | 0 | SOH | 001 |
STX | 002 | ETX | 003 |
EOT | 004 | ENQ | 005 |
ACK | 006 | BEL | 007 |
alert | 007 | BS | 010 |
backspace | '\b' | HT | 011 |
tab | '\t' | LF | 012 |
newline | '\n' | VT | 013 |
vertical-tab | '\v' | FF | 014 |
form-feed | '\f' | CR | 015 |
carriage-return | '\r' | SO | 016 |
SI | 017 | DLE | 020 |
DC1 | 021 | DC2 | 022 |
DC3 | 023 | DC4 | 024 |
NAK | 025 | SYN | 026 |
ETB | 027 | CAN | 030 |
EM | 031 | SUB | 032 |
ESC | 033 | IS4 | 034 |
FS | 034 | IS3 | 035 |
GS | 035 | IS2 | 036 |
RS | 036 | IS1 | 037 |
US | 037 | space | ' ' |
exclamation-mark | '!' | quotation-mark | '"' |
number-sign | '#' | dollar-sign | '$' |
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, then
[[=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.
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
Name | Description |
---|---|
ABS() | Return the absolute value |
ACOS() | Return the arc cosine |
ASIN() | Return the arc sine |
ATAN2() , ATAN() | Return the arc tangent of the two arguments |
ATAN() | Return the arc tangent |
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() (v4.1.0) | Compute a cyclic redundancy check value |
DEGREES() | Convert radians to degrees |
DIV (v4.1.0) | Integer division |
/ | Division operator |
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 |
LOG10() | Return the base-10 logarithm of the argument |
LOG2() | Return the base-2 logarithm of the argument |
LOG() | Return the natural logarithm of the first argument |
- | Minus operator |
MOD() | Return the remainder |
% | Modulo operator |
OCT() | Return an octal representation of a decimal number |
PI() | Return the value of pi |
+ | Addition operator |
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 |
* | Times operator |
TRUNCATE() | Truncate to specified number of decimal places |
- | Change the sign of the argument |
Name | Description |
---|---|
DIV (v4.1.0) | Integer division |
/ | Division operator |
- | Minus operator |
% | Modulo operator |
+ | Addition operator |
* | Times operator |
- | Change the sign of the argument |
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 arguments are integers.
If one of the arguments is an unsigned integer, and the other argument is also an integer, the result is an unsigned integer.
If any of the operands of a
+
,
-
,
/
,
*
,
%
is a
real or string value, then the precision of the result is
the precision of the argument with the maximum precision.
In division performed with
/
, the
scale of the result when using two exact values is the scale
of the first argument 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)
, would
resolve 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 sub-components of a calculation use the appropriate level of precision. See Section 11.9, “Cast Functions and Operators”.
Addition:
mysql> SELECT 3+5;
-> 8
Subtraction:
mysql> SELECT 3-5;
-> -2
Unary minus. This operator changes the sign of the argument.
mysql> SELECT - 2;
-> -2
If this operator is used with a BIGINT
,
the return value is also a BIGINT
. This
means that you should avoid using
–
on integers that may have the
value of –263.
Multiplication:
mysql>SELECT 3*5;
-> 15 mysql>SELECT 18014398509481984*18014398509481984.0;
-> 324518553658426726783156020576256.0 mysql>SELECT 18014398509481984*18014398509481984;
-> 0
The result of the last expression is incorrect because the
result of the integer multiplication exceeds the 64-bit
range of BIGINT
calculations. (See
Section 10.2, “Numeric 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. Similar to
FLOOR()
, but is safe with
BIGINT
values.
mysql> SELECT 5 DIV 2;
-> 2
Modulo operation. Returns the remainder of
N
divided by
M
. For more information, see the
description for the MOD()
function in Section 11.5.2, “Mathematical Functions”.
Name | Description |
---|---|
ABS() | Return the absolute value |
ACOS() | Return the arc cosine |
ASIN() | Return the arc sine |
ATAN2() , ATAN() | Return the arc tangent of the two arguments |
ATAN() | Return the arc tangent |
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() (v4.1.0) | 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 |
LOG10() | Return the base-10 logarithm of the argument |
LOG2() | Return the base-2 logarithm of the argument |
LOG() | Return the natural logarithm of the first argument |
MOD() | Return the remainder |
OCT() | Return an octal representation of a decimal number |
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 to_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'+0xa,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);
-> NULL
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
.
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);
-> 1 mysql>SELECT FLOOR(-1.23);
-> -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 11.4, “String Functions”.
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 11.4, “String Functions”, for details.
Returns the natural logarithm of
X
; that is, the
base-e logarithm of
X
.
mysql>SELECT LN(2);
-> 0.69314718055995 mysql>SELECT LN(-2);
-> NULL
This function is synonymous with
LOG(
.
X
)
If called with one parameter, this function returns the
natural logarithm of X
.
mysql>SELECT LOG(2);
-> 0.69314718055995 mysql>SELECT LOG(-2);
-> NULL
If called with two parameters, this function returns the
logarithm of X
for an arbitrary
base B
.
mysql>SELECT LOG(2,65536);
-> 16 mysql>SELECT LOG(10,100);
-> 2
LOG(
is equivalent to
B
,X
)LOG(
.
X
) /
LOG(B
)
Returns the base-2 logarithm of
.
X
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
.
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
. If a constant integer argument
N
is specified, it is used as the
seed value, which produces a repeatable sequence of column
values.
mysql>SELECT RAND();
-> 0.9233482386203 mysql>SELECT RAND(20);
-> 0.15888261251047 mysql>SELECT RAND(20);
-> 0.15888261251047 mysql>SELECT RAND();
-> 0.63553050033332 mysql>SELECT RAND();
-> 0.70100469486881 mysql>SELECT RAND(20);
-> 0.15888261251047
The effect of using a non-constant argument is undefined. As of MySQL 5.0.13, non-constant arguments are disallowed.
To obtain a random integer R
in
the range i
<=
R
<
j
, use the expression
FLOOR(
. For example, to
obtain a random integer in the range the range
i
+ RAND() * (j
–
i
))7
<= R
<
12
, you could use the following
statement:
SELECT FLOOR(7 + (RAND() * 5));
You cannot use a column with
RAND()
values in an
ORDER BY
clause, because ORDER
BY
would evaluate the column multiple times.
However, you can retrieve rows in random order like this:
mysql> SELECT * FROM tbl_name
ORDER BY RAND();
ORDER BY RAND()
combined with
LIMIT
is useful for selecting a random
sample from a set of rows:
mysql>SELECT * FROM table1, table2 WHERE a=b AND c<d
->ORDER BY RAND() LIMIT 1000;
Note that RAND()
in a
WHERE
clause is re-evaluated every time
the WHERE
is executed.
RAND()
is not meant to be a
perfect random generator, but instead is a fast way to
generate ad hoc random
numbers which is portable between platforms for the same
MySQL version.
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 type is the same type as that of 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 |
+------------------+--------------+
Before MySQL 5.0.3, the behavior of
ROUND()
when the argument is
halfway between two integers depends on the C library
implementation. Different implementations round to the
nearest even number, always up, always down, or always
toward zero. If you need one kind of rounding, you should
use a well-defined function such as
TRUNCATE()
or
FLOOR()
instead.
As of MySQL 5.0.3, ROUND()
uses the following rules depending on the type of the first
argument:
For exact-value numbers,
ROUND()
uses the
“round half up” 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 any fractional part
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 Chapter 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 non-negative 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 10.3, “Date and Time 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.
Name | Description |
---|---|
ADDDATE() (v4.1.1) | Add dates |
ADDTIME() (v4.1.1) | Add time |
CONVERT_TZ() (v4.1.3) | Convert from one timezone 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_ADD() | Add two dates |
DATE_FORMAT() | Format date as specified |
DATE_SUB() | Subtract two dates |
DATE() (v4.1.1) | Extract the date part of a date or datetime expression |
DATEDIFF() (v4.1.1) | Subtract two dates |
DAY() (v4.1.1) | Synonym for DAYOFMONTH() |
DAYNAME() (v4.1.21) | Return the name of the weekday |
DAYOFMONTH() | Return the day of the month (1-31) |
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 date as a UNIX timestamp |
GET_FORMAT() (v4.1.1) | Return a date format string |
HOUR() | Extract the hour |
LAST_DAY (v4.1.1) | Return the last day of the month for the argument |
LOCALTIME() , LOCALTIME | Synonym for NOW() |
LOCALTIMESTAMP , LOCALTIMESTAMP() (v4.0.6) | Synonym for NOW() |
MAKEDATE() (v4.1.1) | Create a date from the year and day of year |
MAKETIME (v4.1.1) | MAKETIME() |
MICROSECOND() (v4.1.1) | Return the microseconds from argument |
MINUTE() | Return the minute from the argument |
MONTH() | Return the month from the date passed |
MONTHNAME() (v4.1.21) | 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() (v4.1.1) | Convert a string to a date |
SUBDATE() | When invoked with three arguments a synonym for DATE_SUB() |
SUBTIME() (v4.1.1) | Subtract times |
SYSDATE() | Return the time at which the function executes |
TIME_FORMAT() | Format as time |
TIME_TO_SEC() | Return the argument converted to seconds |
TIME() (v4.1.1) | Extract the time portion of the expression passed |
TIMEDIFF() (v4.1.1) | Subtract time |
TIMESTAMP() (v4.1.1) | With a single argument, this function returns the date or datetime expression. With two arguments, the sum of the arguments |
TIMESTAMPADD() (v5.0.0) | Add an interval to a datetime expression |
TIMESTAMPDIFF() (v5.0.0) | Subtract an interval from a datetime expression |
TO_DAYS() | Return the date argument converted to days |
UNIX_TIMESTAMP() | Return a UNIX timestamp |
UTC_DATE() (v4.1.1) | Return the current UTC date |
UTC_TIME() (v4.1.1) | Return the current UTC time |
UTC_TIMESTAMP() (v4.1.1) | Return the current UTC date and time |
WEEK() | Return the week number |
WEEKDAY() | Return the weekday index |
WEEKOFYEAR() (v4.1.1) | 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
;
Note that 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 routine or trigger and all
sub-routines called by that routine/trigger). 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 connection's current time zone, which is available
as the value of the time_zone
system variable.
In addition, UNIX_TIMESTAMP()
assumes that its argument is a datetime value in the current time
zone. See Section 9.6, “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. 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
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 the discussion
for DATE_ADD()
.
mysql>SELECT DATE_ADD('1998-01-02', INTERVAL 31 DAY);
-> '1998-02-02' mysql>SELECT ADDDATE('1998-01-02', INTERVAL 31 DAY);
-> '1998-02-02'
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('1998-01-02', 31);
-> '1998-02-02'
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('1997-12-31 23:59:59.999999',
->'1 1:1:1.000002');
-> '1998-01-02 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 9.6, “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 10.1.2, “Overview of Date and Time Types”.
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/Moscow'
, the time zone tables
must be properly set up. See
Section 9.6, “MySQL Server Time Zone Support”, for instructions.
If you intend to use
CONVERT_TZ()
while other
tables are locked with LOCK TABLES
, you
must also lock the mysql.time_zone_name
table.
Returns the current date as a value in
'YYYY-MM-DD'
or YYYYMMDD
format, depending on whether the function is used in a string
or numeric context.
mysql>SELECT CURDATE();
-> '1997-12-15' mysql>SELECT CURDATE() + 0;
-> 19971215
CURRENT_DATE
and
CURRENT_DATE()
are synonyms
for CURDATE()
.
Returns the current time as a value in
'HH:MM:SS'
or
HHMMSS.uuuuuu
format, depending on whether
the function is used in a string or numeric context. The value
is expressed in the current time zone.
mysql>SELECT CURTIME();
-> '23:50:26' mysql>SELECT CURTIME() + 0;
-> 235026.000000
CURRENT_TIME
and
CURRENT_TIME()
are synonyms
for CURTIME()
.
CURRENT_TIMESTAMP
,
CURRENT_TIMESTAMP()
CURRENT_TIMESTAMP
and
CURRENT_TIMESTAMP()
are
synonyms for NOW()
.
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('1997-12-31 23:59:59','1997-12-30');
-> 1 mysql>SELECT DATEDIFF('1997-11-30 23:59:59','1997-12-31');
-> -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 a string; it may
start with a “-
” for negative
intervals. unit
is a keyword
indicating the units in which the expression should be
interpreted.
The INTERVAL
keyword and the
unit
specifier are not case
sensitive.
The following table shows the expected form of the
expr
argument for each
unit
value.
unit Value | Expected
expr
Format |
MICROSECOND | MICROSECONDS |
SECOND | SECONDS |
MINUTE | MINUTES |
HOUR | HOURS |
DAY | DAYS |
WEEK | WEEKS |
MONTH | MONTHS |
QUARTER | QUARTERS |
YEAR | YEARS |
SECOND_MICROSECOND | 'SECONDS.MICROSECONDS' |
MINUTE_MICROSECOND | 'MINUTES.MICROSECONDS' |
MINUTE_SECOND | 'MINUTES:SECONDS' |
HOUR_MICROSECOND | 'HOURS.MICROSECONDS' |
HOUR_SECOND | 'HOURS:MINUTES:SECONDS' |
HOUR_MINUTE | 'HOURS:MINUTES' |
DAY_MICROSECOND | 'DAYS.MICROSECONDS' |
DAY_SECOND | 'DAYS HOURS:MINUTES:SECONDS' |
DAY_MINUTE | 'DAYS HOURS:MINUTES' |
DAY_HOUR | 'DAYS HOURS' |
YEAR_MONTH | 'YEARS-MONTHS' |
The values QUARTER
and
WEEK
are available beginning with MySQL
5.0.0.
The return value depends on the arguments:
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 allows any punctuation delimiter in the
expr
format. Those shown in the
table are the suggested delimiters. If the
date
argument is a
DATE
value and your calculations involve
only YEAR
, MONTH
, and
DAY
parts (that is, no time parts), the
result is a DATE
value. Otherwise, the
result is a DATETIME
value.
Date arithmetic also can be performed using
INTERVAL
together with the
+
or
-
operator:
date
+ INTERVALexpr
unit
date
- INTERVALexpr
unit
INTERVAL
is allowed on either
side of the
expr
unit
+
operator
if the expression on the other side is a date or datetime
value. For the
-
operator, INTERVAL
is allowed only on
the right side, because it makes no sense to subtract a date
or datetime value from an interval.
expr
unit
mysql>SELECT '1997-12-31 23:59:59' + INTERVAL 1 SECOND;
-> '1998-01-01 00:00:00' mysql>SELECT INTERVAL 1 DAY + '1997-12-31';
-> '1998-01-01' mysql>SELECT '1998-01-01' - INTERVAL 1 SECOND;
-> '1997-12-31 23:59:59' mysql>SELECT DATE_ADD('1997-12-31 23:59:59',
->INTERVAL 1 SECOND);
-> '1998-01-01 00:00:00' mysql>SELECT DATE_ADD('1997-12-31 23:59:59',
->INTERVAL 1 DAY);
-> '1998-01-01 23:59:59' mysql>SELECT DATE_ADD('1997-12-31 23:59:59',
->INTERVAL '1:1' MINUTE_SECOND);
-> '1998-01-01 00:01:00' mysql>SELECT DATE_SUB('1998-01-01 00:00:00',
->INTERVAL '1 1:1:1' DAY_SECOND);
-> '1997-12-30 22:58:59' mysql>SELECT DATE_ADD('1998-01-01 00:00:00',
->INTERVAL '-1 10' DAY_HOUR);
-> '1997-12-30 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'
If you specify an interval value that is too short (does not
include all the interval parts that would be expected from the
unit
keyword), MySQL assumes that
you have left out the leftmost parts of the interval value.
For example, if you specify a unit
of DAY_SECOND
, the value of
expr
is expected to have days,
hours, minutes, and seconds parts. If you specify a value like
'1:10'
, MySQL assumes that the days and
hours parts are missing and the value represents minutes and
seconds. In other words, '1:10' DAY_SECOND
is interpreted in such a way that it is equivalent to
'1:10' MINUTE_SECOND
. This is analogous to
the way that MySQL interprets TIME
values
as representing elapsed time rather than as a time of day.
Because expr
is treated as a
string, be careful if you specify a non-string value with
INTERVAL
. For example, with an interval
specifier of HOUR_MINUTE
,
6/4
evaluates to 1.5000
and is treated as 1 hour, 5000 minutes:
mysql>SELECT 6/4;
-> 1.5000 mysql>SELECT DATE_ADD('1999-01-01', INTERVAL 6/4 HOUR_MINUTE);
-> '1999-01-04 12:20:00'
To ensure interpretation of the interval value as you expect,
a CAST()
operation may be
used. To treat 6/4
as 1 hour, 5 minutes,
cast it to a DECIMAL
value with a single
fractional digit:
mysql>SELECT CAST(6/4 AS DECIMAL(3,1));
-> 1.5 mysql>SELECT DATE_ADD('1970-01-01 12:00:00',
->INTERVAL CAST(6/4 AS DECIMAL(3,1)) HOUR_MINUTE);
-> '1970-01-01 13:05:00'
If you add to or subtract from a date value something that contains a time part, the result is automatically converted to a datetime value:
mysql>SELECT DATE_ADD('1999-01-01', INTERVAL 1 DAY);
-> '1999-01-02' mysql>SELECT DATE_ADD('1999-01-01', INTERVAL 1 HOUR);
-> '1999-01-01 01:00:00'
If you add MONTH
,
YEAR_MONTH
, or YEAR
and
the resulting date has a day that is larger than the maximum
day for the new month, the day is adjusted to the maximum days
in the new month:
mysql> SELECT DATE_ADD('1998-01-30', INTERVAL 1 MONTH);
-> '1998-02-28'
Date arithmetic operations require complete dates and do not
work with incomplete dates such as
'2006-07-00'
or badly malformed dates:
mysql>SELECT DATE_ADD('2006-07-00', INTERVAL 1 DAY);
-> NULL mysql>SELECT '2005-03-32' + INTERVAL 1 MONTH;
-> NULL
Formats the date
value according to
the format
string.
The following specifiers may be used in the
format
string. The
“%
” character is required
before format specifier characters.
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 |
%u | Week (00 ..53 ), where Monday is the
first day of the week |
%V | Week (01 ..53 ), where Sunday is the
first day of the week; used with %X |
%v | Week (01 ..53 ), where Monday is the
first day of the week; 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 allows the storing of incomplete dates
such as '2004-00-00'
.
As of MySQL 5.0.25, the language used for day and month names
and abbreviations is controlled by the value of the
lc_time_names
system variable
(Section 9.7, “MySQL Server Locale Support”).
As of MySQL 5.0.36,
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.
Before 5.0.36, the return value is a binary string.
mysql>SELECT DATE_FORMAT('1997-10-04 22:23:00', '%W %M %Y');
-> 'Saturday October 1997' mysql>SELECT DATE_FORMAT('1997-10-04 22:23:00', '%H:%i:%s');
-> '22:23:00' mysql>SELECT DATE_FORMAT('1997-10-04 22:23:00',
'%D %y %a %d %m %b %j'); -> '4th 97 Sat 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
. As of MySQL 5.0.25, the
language used for the name is controlled by the value of the
lc_time_names
system variable
(Section 9.7, “MySQL Server Locale Support”).
mysql> SELECT DAYNAME('1998-02-05');
-> 'Thursday'
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('1998-02-03');
-> 3
Returns the weekday index for date
(1
= Sunday, 2
= Monday,
…, 7
= Saturday). These index values
correspond to the ODBC standard.
mysql> SELECT DAYOFWEEK('1998-02-03');
-> 3
Returns the day of the year for
date
, in the range
1
to 366
.
mysql> SELECT DAYOFYEAR('1998-02-03');
-> 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.
mysql>SELECT EXTRACT(YEAR FROM '1999-07-02');
-> 1999 mysql>SELECT EXTRACT(YEAR_MONTH FROM '1999-07-02 01:02:03');
-> 199907 mysql>SELECT EXTRACT(DAY_MINUTE FROM '1999-07-02 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(729669);
-> '1997-10-07'
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 11.7, “What Calendar Is Used By MySQL?”.
FROM_UNIXTIME(
,
unix_timestamp
)FROM_UNIXTIME(
unix_timestamp
,format
)
Returns a representation of the
unix_timestamp
argument as a value
in 'YYYY-MM-DD HH:MM:SS'
or
YYYYMMDDHHMMSS.uuuuuu
format, depending on
whether the function is used in a string or numeric context.
The value is expressed in the current time zone.
unix_timestamp
is an internal
timestamp value such as is produced by the
UNIX_TIMESTAMP()
function.
If format
is given, the result is
formatted according to the format
string, which is used the same way as listed in the entry for
the DATE_FORMAT()
function.
mysql>SELECT FROM_UNIXTIME(1196440219);
-> '2007-11-30 10:30:19' mysql>SELECT FROM_UNIXTIME(1196440219) + 0;
-> 20071130103019.000000 mysql>SELECT FROM_UNIXTIME(UNIX_TIMESTAMP(),
->'%Y %D %M %h:%i:%s %x');
-> '2007 30th November 10:30:59 2007'
Note: If you use
UNIX_TIMESTAMP()
and
FROM_UNIXTIME()
to convert
between TIMESTAMP
values 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()
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(2001,31), MAKEDATE(2001,32);
-> '2001-01-31', '2001-02-01' mysql>SELECT MAKEDATE(2001,365), MAKEDATE(2004,365);
-> '2001-12-31', '2004-12-30' mysql>SELECT MAKEDATE(2001,0);
-> NULL
Returns a time value calculated from the
hour
,
minute
, and
second
arguments.
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('1997-12-31 23:59:59.000010');
-> 10
Returns the minute for time
, in the
range 0
to 59
.
mysql> SELECT MINUTE('98-02-03 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('1998-02-03');
-> 2
Returns the full name of the month for
date
. As of MySQL 5.0.25, the
language used for the name is controlled by the value of the
lc_time_names
system variable
(Section 9.7, “MySQL Server Locale Support”).
mysql> SELECT MONTHNAME('1998-02-05');
-> 'February'
Returns the current date and time as a value in
'YYYY-MM-DD HH:MM:SS'
or
YYYYMMDDHHMMSS.uuuuuu
format, depending on
whether the function is used in a string or numeric context.
The value is expressed in the current time zone.
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 routine or trigger,
NOW()
returns the time at
which the routine or triggering statement began to execute.)
This differs from the behavior for
SYSDATE()
, which returns the
exact time at which it executes as of MySQL 5.0.13.
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()
.
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
. Note that the
period argument P
is
not a date value.
mysql> SELECT PERIOD_ADD(9801,2);
-> 199803
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(9802,199703);
-> 11
Returns the quarter of the year for
date
, in the range
1
to 4
.
mysql> SELECT QUARTER('98-04-01');
-> 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.
The date, time, or datetime values contained in
str
should be given in the format
indicated by format
. For the
specifiers that can be used in
format
, see the
DATE_FORMAT()
function
description. If str
contains an
illegal date, time, or datetime value,
STR_TO_DATE()
returns
NULL
. Starting from MySQL 5.0.3, an illegal
value also produces a warning.
Range checking on the parts of date values is as described in
Section 10.3.1, “The DATETIME
, DATE
, and
TIMESTAMP
Types”. This means, for example, that
“zero” dates or dates with part values of 0 are
allowed 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'
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, then 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('1998-01-02', INTERVAL 31 DAY);
-> '1997-12-02' mysql>SELECT SUBDATE('1998-01-02', INTERVAL 31 DAY);
-> '1997-12-02'
The second form allows 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('1998-01-02 12:00:00', 31);
-> '1997-12-02 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('1997-12-31 23:59:59.999999','1 1:1:1.000002');
-> '1997-12-30 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
'YYYY-MM-DD HH:MM:SS'
or
YYYYMMDDHHMMSS.uuuuuu
format, depending on
whether the function is used in a string or numeric context.
As of MySQL 5.0.13, 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 routine or
trigger, NOW()
returns the
time at which the routine 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
non-deterministic and therefore unsafe for replication. If
that is a problem, you can start the server with the
--sysdate-is-now
option to cause
SYSDATE()
to be an alias for
NOW()
. The non-deterministic
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.
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.
mysql>SELECT TIMEDIFF('2000:01:01 00:00:00',
->'2000:01:01 00:00:00.000001');
-> '-00:00:00.000001' mysql>SELECT TIMEDIFF('1997-12-31 23:59:59.000001',
->'1997-12-30 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: FRAC_SECOND
(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'
TIMESTAMPADD()
is available as
of MySQL 5.0.0.
TIMESTAMPDIFF(
unit
,datetime_expr1
,datetime_expr2
)
Returns the integer difference between the date or datetime
expressions datetime_expr1
and
datetime_expr2
. The unit for the
result 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
TIMESTAMPDIFF()
is available
as of MySQL 5.0.0.
This is used like the
DATE_FORMAT()
function, but
the format
string may contain
format specifiers only for hours, minutes, and seconds. 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('1997-10-07');
-> 729669
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 11.7, “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 10.3, “Date and Time Types”. For example,
'1997-10-07'
and
'97-10-07'
are seen as identical dates:
mysql> SELECT TO_DAYS('1997-10-07'), TO_DAYS('97-10-07');
-> 729669, 729669
UNIX_TIMESTAMP()
,
UNIX_TIMESTAMP(
date
)
If called with no argument, returns a Unix timestamp (seconds
since '1970-01-01 00:00:00'
UTC) as an
unsigned integer. 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.
date
may be a
DATE
string, a DATETIME
string, a TIMESTAMP
, or a number in the
format YYMMDD
or
YYYYMMDD
. The server interprets
date
as a value in the current time
zone and converts it to an internal value in UTC. Clients can
set their time zone as described in
Section 9.6, “MySQL Server Time Zone Support”.
mysql>SELECT UNIX_TIMESTAMP();
-> 1196440210 mysql>SELECT UNIX_TIMESTAMP('2007-11-30 10:30:19');
-> 1196440219
When UNIX_TIMESTAMP()
is used
on a TIMESTAMP
column, the function returns
the internal timestamp value directly, with no implicit
“string-to-Unix-timestamp” conversion. If you
pass an out-of-range date to
UNIX_TIMESTAMP()
, it returns
0
.
Note: If you use
UNIX_TIMESTAMP()
and
FROM_UNIXTIME()
to convert
between TIMESTAMP
values 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, it is possible for two
UNIX_TIMESTAMP()
to map two
TIMESTAMP
values to the same Unix timestamp
value. FROM_UNIXTIME()
will
map that value back to only one of the original
TIMESTAMP
values. Here is an example, using
TIMESTAMP
values in the
CET
time zone:
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 | +---------------------------+
If you want to subtract
UNIX_TIMESTAMP()
columns, you
might want to cast the result to signed integers. See
Section 11.9, “Cast Functions and Operators”.
Returns the current UTC date as a value in
'YYYY-MM-DD'
or YYYYMMDD
format, depending on whether the function is used in a 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.uuuuuu
format, depending on whether
the function is used in a string or numeric context.
mysql> SELECT UTC_TIME(), UTC_TIME() + 0;
-> '18:07:53', 180753.000000
UTC_TIMESTAMP
,
UTC_TIMESTAMP()
Returns the current UTC date and time as a value in
'YYYY-MM-DD HH:MM:SS'
or
YYYYMMDDHHMMSS.uuuuuu
format, depending on
whether the function is used in a string or numeric context.
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()
allows 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 5.1.3, “System Variables”.
The following table describes how the
mode
argument works.
First day | |||
Mode | of week | Range | Week 1 is the first week … |
0 | Sunday | 0-53 | with a Sunday in this year |
1 | Monday | 0-53 | with more than 3 days this year |
2 | Sunday | 1-53 | with a Sunday in this year |
3 | Monday | 1-53 | with more than 3 days this year |
4 | Sunday | 0-53 | with more than 3 days this year |
5 | Monday | 0-53 | with a Monday in this year |
6 | Sunday | 1-53 | with more than 3 days this year |
7 | Monday | 1-53 | with a Monday in this year |
mysql>SELECT WEEK('1998-02-20');
-> 7 mysql>SELECT WEEK('1998-02-20',0);
-> 7 mysql>SELECT WEEK('1998-02-20',1);
-> 8 mysql>SELECT WEEK('1998-12-31',1);
-> 53
Note that 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 MySQL should return 52
for the WEEK()
function,
because the given date actually occurs in the 52nd week of
1999. We decided to return 0
instead
because we want the function to return “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 would prefer the result to be 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('1998-02-03 22:23:00');
-> 1 mysql>SELECT WEEKDAY('1997-11-05');
-> 2
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('1998-02-20');
-> 8
Returns the year for date
, in the
range 1000
to 9999
, or
0
for the “zero” date.
mysql> SELECT YEAR('98-02-03');
-> 1998
YEARWEEK(
,
date
)YEARWEEK(
date
,mode
)
Returns year and week for a date. The
mode
argument works exactly like
the mode
argument to
WEEK()
. 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.
mysql> SELECT YEARWEEK('1987-01-01');
-> 198653
Note that 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.
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 non-existent.
A calendar applied to dates when it wasn't 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 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
MyISAM
tables, and can be created only for
CHAR
, VARCHAR
, or
TEXT
columns.
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 literal string, not a variable or a
column name. There are three types of 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. Common words such as “some” or
“then” are stopwords and do not match if present
in the search string. The IN BOOLEAN MODE
modifier specifies a boolean search. For more information, see
Section 11.8.2, “Boolean 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. The stopword list applies. In addition, words that are present in 50% or more of the rows are considered common and do not match. Full-text searches are natural language searches if no modifier is given.
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 WITH QUERY EXPANSION
modifier specifies a query expansion search. For more
information, see Section 11.8.3, “Full-Text Searches with Query Expansion”.
Constraints on full-text searching are listed in Section 11.8.5, “Full-Text Restrictions”.
By default, 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)
->);
Query OK, 0 rows affected (0.00 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 (0.00 sec) Records: 6 Duplicates: 0 Warnings: 0 mysql>SELECT * FROM articles
->WHERE MATCH (title,body) AGAINST ('database');
+----+-------------------+------------------------------------------+ | id | title | body | +----+-------------------+------------------------------------------+ | 5 | MySQL vs. YourSQL | In the following database comparison ... | | 1 | MySQL Tutorial | DBMS stands for DataBase ... | +----+-------------------+------------------------------------------+ 2 rows in set (0.00 sec)
By default, the search is performed in case-insensitive fashion.
However, you can perform a case-sensitive full-text search by
using 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 non-negative
floating-point numbers. Zero relevance means no similarity.
Relevance is computed based on the number of words in the row,
the number of unique words in that row, the total number of
words in the collection, and the number of documents (rows) that
contain a particular word.
To simply count matches, you could use a query like this:
mysql>SELECT COUNT(*) FROM articles
->WHERE MATCH (title,body)
->AGAINST ('database');
+----------+ | COUNT(*) | +----------+ | 2 | +----------+ 1 row in set (0.00 sec)
However, you might find it quicker to rewrite the query as follows:
mysql>SELECT
->COUNT(IF(MATCH (title,body) AGAINST ('database'), 1, NULL))
->AS count
->FROM articles;
+-------+ | count | +-------+ | 2 | +-------+ 1 row in set (0.00 sec)
The first query sorts the results by relevance whereas the second does not. However, the second query performs a full table scan and the first does not. The first may be faster if the search matches few rows; otherwise, the second may be faster because it would read many rows anyway.
For natural-language full-text searches, it is a requirement
that the columns named in the
MATCH()
function 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. If you wanted to search the title
or
body
separately, you would need to create
separate FULLTEXT
indexes for each column.
It is also possible to perform a boolean search or a search with query expansion. These search types are described in Section 11.8.2, “Boolean Full-Text Searches”, and Section 11.8.3, “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. 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')
->FROM articles;
+----+-----------------------------------------+ | id | MATCH (title,body) AGAINST ('Tutorial') | +----+-----------------------------------------+ | 1 | 0.65545833110809 | | 2 | 0 | | 3 | 0.66266459226608 | | 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, you should 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') AS score
->FROM articles WHERE MATCH (title,body) AGAINST
->('Security implications of running MySQL as root');
+----+-------------------------------------+-----------------+ | 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)
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 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
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, you
must preprocess them so that they are separated by some
arbitrary delimiter such as “"
”.
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 four characters.
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 overwritten by a user-defined list.
The default stopword list is given in Section 11.8.4, “Full-Text Stopwords”. The default minimum word length and stopword list can be changed as described in Section 11.8.6, “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. Consequently, a word that is present in many documents has a lower weight (and may even have a zero 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.
Such a technique works best with large collections (in fact, it
was carefully tuned this way). For very small tables, word
distribution does not adequately reflect their semantic value,
and this model may sometimes produce bizarre results. For
example, although the word “MySQL” is present in
every row of the articles
table shown
earlier, a search for the word produces no results:
mysql>SELECT * FROM articles
->WHERE MATCH (title,body) AGAINST ('MySQL');
Empty set (0.00 sec)
The search result is empty because the word “MySQL” is present in at least 50% of the rows. As such, it is effectively treated as a stopword. For large data sets, this is the most desirable behavior: A natural language query should not return every second row from a 1GB table. For small data sets, it may be less desirable.
A word that matches half of the rows in a table is less likely to locate relevant documents. In fact, it most likely finds plenty of irrelevant documents. We all know this happens far too often when we are trying to find something on the Internet with a search engine. It is with this reasoning that rows containing the word are assigned a low semantic value for the particular data set in which they occur. A given word may reach the 50% threshold in one data set but not another.
The 50% threshold has a significant implication when you first try full-text searching to see how it works: If you create a 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. Be sure to insert at least three rows, and preferably many more. Users who need to bypass the 50% limitation can use the boolean search mode; see Section 11.8.2, “Boolean Full-Text Searches”.
MySQL can perform boolean full-text searches using the
IN BOOLEAN MODE
modifier:
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 ... | +----+-----------------------+-------------------------------------+
The +
and -
operators
indicate that a word is required to be present or absent,
respectively, for a match to occur. Thus, this query retrieves
all the rows that contain the word “MySQL” but that
do not contain the word
“YourSQL”.
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 use the 50% threshold.
They do not automatically sort rows in order of decreasing relevance. You can see this from the preceding query result: The row with the highest relevance is the one that contains “MySQL” twice, but it is listed last, not first.
They 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.
The stopword list applies.
The boolean full-text search capability supports the following operators:
+
A leading plus sign indicates that this word must be present in each row that is returned.
-
A leading minus sign indicates that this word must not be present in any of the rows that are returned.
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.
> <
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 should be
appended to the word to be affected.
Words match if they begin with the word preceding the
*
operator.
If a stopword or too-short word is specified with the
truncation operator, it will not be stripped from a boolean
query. For example, a search for '+word
+stopword*'
will likely return fewer rows than a
search for '+word +stopword'
because the
former query remains as is and requires
stopword*
to be present in a document.
The latter query is transformed to +word
.
"
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, performs a search in the
FULLTEXT
index for the words. Prior to
MySQL 5.0.3, the engine then performed a substring search
for the phrase in the records that were found, so the match
must include non-word characters in the phrase. As of MySQL
5.0.3, non-word 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"
in MySQL 5.0.3, but not
before.
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 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 quotes that enclose the search string
itself.
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
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');
+----+-------------------+------------------------------------------+ | id | title | body | +----+-------------------+------------------------------------------+ | 5 | MySQL vs. YourSQL | In the following database comparison ... | | 1 | MySQL Tutorial | DBMS stands for DataBase ... | +----+-------------------+------------------------------------------+ 2 rows in set (0.00 sec) mysql>SELECT * FROM articles
->WHERE MATCH (title,body)
->AGAINST ('database' WITH QUERY EXPANSION);
+----+-------------------+------------------------------------------+ | id | title | body | +----+-------------------+------------------------------------------+ | 1 | MySQL Tutorial | DBMS stands for DataBase ... | | 5 | MySQL vs. YourSQL | In the following database comparison ... | | 3 | Optimizing MySQL | In this tutorial we will show ... | +----+-------------------+------------------------------------------+ 3 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 non-relevant documents, it is meaningful to use only when a search phrase is rather short.
The following table shows the default list of full-text stopwords.
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 | knows | known | 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 |
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
MyISAM
tables only.
Full-text searches can be used with most multi-byte
character sets. The exception is that for Unicode, the
utf8
character set can be used, but not
the ucs2
character set. However, 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.
Ideographic languages such as Chinese and Japanese do not
have word delimiters. Therefore, the
FULLTEXT
parser cannot
determine where words begin and end in these and other such
languages. The implications of this and some
workarounds for the problem are described in
Section 11.8, “Full-Text Search Functions”.
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
. Boolean-mode searches
can be done on non-indexed columns, although they are likely
to be slow.
The argument to AGAINST()
must be a
constant string.
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 2.4.15, “MySQL Installation Using a Source Distribution”.
Note that full-text search is carefully tuned for the most 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 this are given at the end of this section.
The minimum and maximum lengths of words to be indexed are
defined by the ft_min_word_len
and
ft_max_word_len
system variables. (See
Section 5.1.3, “System Variables”.) The default
minimum value is four characters; the default maximum is
version dependent. If you change either value, you must
rebuild your FULLTEXT
indexes. For
example, if you want three-character words to be searchable,
you can set the ft_min_word_len
variable
by putting the following lines in an option file:
[mysqld] ft_min_word_len=3
Then you must restart the server and rebuild your
FULLTEXT
indexes. Note particularly the
remarks regarding myisamchk in the
instructions following this list.
To override the default stopword list, set the
ft_stopword_file
system variable. (See
Section 5.1.3, “System Variables”.) The variable
value should be the pathname of the file containing the
stopword list, or the empty string to disable stopword
filtering. 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. That is, you may use any
non-alphanumeric character such as newline, space, or comma
to separate stopwords. 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 9.1.3.1, “Server Character Set and Collation”.
The 50% threshold for natural language searches is
determined by the particular weighting scheme chosen. To
disable it, look for the following line in
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,
set the ft_boolean_syntax
system
variable. This variable can be changed while the server is
running, but you must have the SUPER
privilege to do so. No rebuilding of indexes is necessary in
this case. See Section 5.1.3, “System Variables”,
which describes the rules governing how to set this
variable.
If you want to change the set of characters that are considered word characters, you can do so in two ways. Suppose that you want to treat the hyphen character ('-') as a word character. Use either of these methods:
Modify the MySQL source: In
myisam/ftdefs.h
, 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
<ctype><map>
contents in
one of the character set XML files to specify that
'-'
is a “letter.” Then
use the given character set for your
FULLTEXT
indexes.
After making the modification, you must rebuild the indexes
for each table that contains any FULLTEXT
indexes.
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 indexes in this case, it
is sufficient to do a QUICK
repair operation:
mysql> REPAIR TABLE tbl_name
QUICK;
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.
Note that if you use myisamchk to perform an
operation that modifies 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 to
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:
shell> 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 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.
Name | Description |
---|---|
BINARY | Cast a string to a binary string |
CAST() | Cast a value as a certain type |
Convert() | Cast a value as a certain type |
The BINARY
operator casts
the string following it to a binary string. This is an easy
way to force a column comparison to be done byte by byte
rather than character by character. This causes the comparison
to be case sensitive even if the column isn't defined as
BINARY
or BLOB
.
BINARY
also causes trailing
spaces to be significant.
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.
BINARY
is shorthand for
str
CAST(
.
str
AS
BINARY)
Note that in some contexts, if you cast an indexed column to
BINARY
, MySQL is not able to use the index
efficiently.
The CAST()
function takes a
value of one type and produce a value of another type, similar
to CONVERT()
. See the
description of CONVERT()
for
more information.
CONVERT(
,
expr
,type
)CONVERT(
expr
USING transcoding_name
)
The CONVERT()
and
CAST()
functions take a value
of one type and produce a value of another type.
The type
can be one of the
following values:
BINARY[(
N
)]
CHAR[(
N
)]
DATE
DATETIME
DECIMAL
SIGNED [INTEGER]
TIME
UNSIGNED [INTEGER]
BINARY
produces a string with the
BINARY
data type. See
Section 10.4.2, “The BINARY
and VARBINARY
Types” for a description of how
this affects comparisons. If the optional length
N
is given,
BINARY(
causes
the cast to use no more than N
)N
bytes of the argument. As of MySQL 5.0.17, values shorter than
N
bytes are padded with
0x00
bytes to a length of
N
.
CHAR(
causes the cast to use no more than
N
)N
characters of the argument.
The DECIMAL
type is available as of MySQL
5.0.8.
CAST()
and
CONVERT(... USING ...)
are
standard SQL syntax. The non-USING
form of
CONVERT()
is ODBC syntax.
CONVERT()
with
USING
is used to convert 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);
Normally, you cannot compare a BLOB
value or
other binary string in case-insensitive fashion because binary
strings have no character set, and thus no concept of lettercase.
To perform a case-insensitive comparison, use the
CONVERT()
function to convert the
value to a non-binary string. If the character set of the result
has a case-insensitive collation, the
LIKE
operation is not case
sensitive:
SELECT 'A' LIKE CONVERT(blob_col
USING latin1) FROMtbl_name
;
To use a different character set, substitute its name for
latin1
in the preceding statement. To ensure
that a case-insensitive collation is used, specify a
COLLATE
clause following the
CONVERT()
call.
CONVERT()
can be used more
generally for comparing strings that are represented in different
character sets.
The cast functions are useful when you want to create a column
with a specific type in a CREATE ... SELECT
statement:
CREATE TABLE new_table SELECT CAST('2000-01-01' AS DATE);
The functions also can be 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(
is the same thing as
str
AS
BINARY)BINARY
.
str
CAST(
treats the expression as a string with the
default character set.
expr
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))
.
You should not use CAST()
to
extract data in different formats but instead use string functions
like LEFT()
or
EXTRACT()
. See
Section 11.6, “Date and Time Functions”.
To cast a string to a numeric value in numeric context, you normally do not have to do anything other than to use the string value as though it were a number:
mysql> SELECT 1+'1';
-> 2
If you use a number in string context, the number automatically is
converted to a BINARY
string.
mysql> SELECT CONCAT('hello you ',2);
-> 'hello you 2'
MySQL supports arithmetic with both signed and unsigned 64-bit
values. If you are using numeric operators (such as
+
or
-
) and one of
the operands is an unsigned integer, the result is unsigned. You
can override this by using the SIGNED
and
UNSIGNED
cast operators to cast the operation
to a signed or unsigned 64-bit integer, respectively.
mysql>SELECT CAST(1-2 AS UNSIGNED)
-> 18446744073709551615 mysql>SELECT CAST(CAST(1-2 AS UNSIGNED) AS SIGNED);
-> -1
Note that 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
If you are using a string in an arithmetic operation, this is converted to a floating-point number.
If you convert a “zero” date string to a date,
CONVERT()
and
CAST()
return
NULL
when the NO_ZERO_DATE
SQL mode is enabled. As of MySQL 5.0.4, they also produce a
warning.
Name | Description |
---|---|
AES_DECRYPT() | Decrypt using AES |
AES_ENCRYPT() | Encrypt using AES |
BENCHMARK() | Repeatedly execute an expression |
BIT_COUNT() | Return the number of bits that are set |
& | Bitwise AND |
~ | Invert bits |
| | Bitwise OR |
^ | Bitwise XOR |
CHARSET() (v4.1.0) | Return the character set of the argument |
COERCIBILITY() (v4.1.1) | Return the collation coercibility value of the string argument |
COLLATION() (v4.1.0) | Return the collation of the string argument |
COMPRESS() (v4.1.1) | Return result as a binary string |
CONNECTION_ID() | Return the connection ID (thread ID) for the connection |
CURRENT_USER() , CURRENT_USER | Return the username and hostname combination |
DATABASE() | Return the default (current) database name |
DECODE() | Decodes a string encrypted using ENCODE() |
DEFAULT() | Return the default value for a table column |
DES_DECRYPT() | Decrypt a string |
DES_ENCRYPT() | Encrypt a string |
ENCODE() | Encode a string |
ENCRYPT() | Encrypt a string |
FOUND_ROWS() | For a SELECT with a LIMIT clause, the number of rows that would be returned were there no LIMIT clause |
GET_LOCK() | Get a named lock |
INET_ATON() | Return the numeric value of an IP address |
INET_NTOA() | Return the IP address from a numeric value |
IS_FREE_LOCK() | Checks whether the named lock is free |
IS_USED_LOCK() (v4.1.0) | Checks whether the named lock is in use. Return connection identifier if true. |
LAST_INSERT_ID() | Value of the AUTOINCREMENT column for the last INSERT |
<< | Left shift |
MASTER_POS_WAIT() | Block until the slave has read and applied all updates up to the specified position |
MD5() | Calculate MD5 checksum |
NAME_CONST() (v5.0.12) | Causes the column to have the given name |
OLD_PASSWORD() (v4.1) | Return the value of the old (pre-4.1) implementation of PASSWORD |
PASSWORD() | Calculate and return a password string |
RAND() | Return a random floating-point value |
RELEASE_LOCK() | Releases the named lock |
>> | Right shift |
ROW_COUNT() (v5.0.1) | The number of rows updated |
SCHEMA() (v5.0.2) | A synonym for DATABASE() |
SESSION_USER() | Synonym for USER() |
SHA1() , SHA() | Calculate an SHA-1 160-bit checksum |
SLEEP() (v5.0.12) | Sleep for a number of seconds |
SYSTEM_USER() | Synonym for USER() |
UNCOMPRESS() (v4.1.1) | Uncompress a string compressed |
UNCOMPRESSED_LENGTH() (v4.1.1) | Return the length of a string before compression |
USER() | Return the current username and hostname |
UUID() (v4.1.2) | Return a Universal Unique Identifier (UUID) |
VALUES() (v4.1.1) | Defines the values to be used during an INSERT |
VERSION() | Returns a string that indicates the MySQL server version |
Name | Description |
---|---|
BIT_COUNT() | Return the number of bits that are set |
& | Bitwise AND |
~ | Invert bits |
| | Bitwise OR |
^ | Bitwise XOR |
<< | Left shift |
>> | Right shift |
MySQL uses BIGINT
(64-bit) arithmetic for bit
operations, so these operators have a maximum range of 64 bits.
Bitwise OR:
mysql> SELECT 29 | 15;
-> 31
The result is an unsigned 64-bit integer.
Bitwise AND:
mysql> SELECT 29 & 15;
-> 13
The result is an unsigned 64-bit integer.
Bitwise XOR:
mysql>SELECT 1 ^ 1;
-> 0 mysql>SELECT 1 ^ 0;
-> 1 mysql>SELECT 11 ^ 3;
-> 8
The result is an unsigned 64-bit integer.
Shifts a longlong (BIGINT
) number to the
left.
mysql> SELECT 1 << 2;
-> 4
The result is an unsigned 64-bit integer.
Shifts a longlong (BIGINT
) number to the
right.
mysql> SELECT 4 >> 2;
-> 1
The result is an unsigned 64-bit integer.
Invert all bits.
mysql> SELECT 5 & ~1;
-> 4
The result is an unsigned 64-bit integer.
Returns the number of bits that are set in the argument
N
.
mysql> SELECT BIT_COUNT(29), BIT_COUNT(b'101010');
-> 4, 3
Name | Description |
---|---|
AES_DECRYPT() | Decrypt using AES |
AES_ENCRYPT() | Encrypt using AES |
COMPRESS() (v4.1.1) | Return result as a binary string |
DECODE() | Decodes a string encrypted using ENCODE() |
DES_DECRYPT() | Decrypt a string |
DES_ENCRYPT() | Encrypt a string |
ENCODE() | Encode a string |
ENCRYPT() | Encrypt a string |
MD5() | Calculate MD5 checksum |
OLD_PASSWORD() (v4.1) | Return the value of the old (pre-4.1) implementation of PASSWORD |
PASSWORD() | Calculate and return a password string |
SHA1() , SHA() | Calculate an SHA-1 160-bit checksum |
UNCOMPRESS() (v4.1.1) | Uncompress a string compressed |
UNCOMPRESSED_LENGTH() (v4.1.1) | Return the length of a string before compression |
The encryption and compression functions return binary
strings. For many of these functions, the result might contain
arbitrary byte values. If you want to store these results, use
a BLOB
column rather than a
CHAR
or (before MySQL 5.0.3)
VARCHAR
column to avoid potential problems
with trailing space removal that would change data values.
Exploits for the MD5 and SHA-1 algorithms have become known. You may wish to consider using one of the other encryption functions described in this section instead.
AES_DECRYPT(
crypt_str
,key_str
)
This function allows decryption of data using the official
AES (Advanced Encryption Standard) algorithm. For more
information, see the description of
AES_ENCRYPT()
.
AES_ENCRYPT()
and
AES_DECRYPT()
allow
encryption and decryption of data using the official AES
(Advanced Encryption Standard) algorithm, previously known
as “Rijndael.” Encoding with a 128-bit key
length is used, but you can extend it up to 256 bits by
modifying the source. We chose 128 bits because it is much
faster and it is secure enough for most purposes.
AES_ENCRYPT()
encrypts a
string and returns a binary string.
AES_DECRYPT()
decrypts the
encrypted string and returns the original string. The input
arguments may be any length. If either argument is
NULL
, the result of this function is also
NULL
.
Because AES is a block-level algorithm, padding is used to encode uneven length strings and so the result string length may be calculated using this formula:
16 × (trunc(string_length
/ 16) + 1)
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.
You can use the AES functions to store data in an encrypted form by modifying your queries:
INSERT INTO t VALUES (1,AES_ENCRYPT('text','password'));
AES_ENCRYPT()
and
AES_DECRYPT()
can be
considered the most cryptographically secure encryption
functions currently available in MySQL.
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.
Non-empty strings are stored as a four-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. (Use of
CHAR
or VARCHAR
to
store compressed strings is not recommended. It is
better to use a BLOB
column instead.)
Decrypts the encrypted string
crypt_str
using
pass_str
as the password.
crypt_str
should be a string
returned from ENCODE()
.
Encrypt str
using
pass_str
as the password. To
decrypt the result, use
DECODE()
.
The result is a binary string of the same length as
str
.
The strength of the encryption is based on how good the random generator is. It should suffice for short strings.
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 5.5.7, “Using Secure 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
.
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 5.5.7, “Using Secure Connections”.
The encryption key to use is chosen based on the second
argument to DES_ENCRYPT()
,
if one was given:
Argument | Description |
No argument | The first key from the DES key file is used. |
key_num | The given key number (0-9) from the DES key file is used. |
key_str | 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.
mysql>SELECT customer_address FROM customer_table
>WHERE crypted_credit_card = DES_ENCRYPT('credit_card_number');
Encrypts str
using the Unix
crypt()
system call and returns a
binary string. The salt
argument
should be a string with at least two characters. If no
salt
argument is given, a random
value is used.
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
multi-byte character sets other than utf8
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 binary string of 32 hex digits, or
NULL
if the argument was
NULL
. The return value can, for example,
be used as a hash key.
mysql> SELECT MD5('testing');
-> 'ae2b1fca515949e5d54fb22b8ed95575'
This is the “RSA Data Security, Inc. MD5 Message-Digest Algorithm.”
If you want to convert the value to uppercase, see the
description of binary string conversion given in the entry
for the BINARY
operator in
Section 11.9, “Cast Functions and Operators”.
See the note regarding the MD5 algorithm at the beginning this section.
OLD_PASSWORD()
was added to
MySQL when the implementation of
PASSWORD()
was changed to
improve security.
OLD_PASSWORD()
returns the
value of the old (pre-4.1) implementation of
PASSWORD()
as a binary
string, and is intended to permit you to reset passwords for
any pre-4.1 clients that need to connect to your version
5.0 MySQL server without locking them out. See
Section 5.4.9, “Password Hashing as of MySQL 4.1”.
Calculates and returns a password string from the plaintext
password str
and returns a binary
string, or NULL
if the argument was
NULL
. This is the function that is used
for encrypting MySQL passwords for storage in the
Password
column of the
user
grant table.
mysql> SELECT PASSWORD('badpwd');
-> '*AAB3E285149C0135D51A520E1940DD3263DC008C'
PASSWORD()
encryption is
one-way (not reversible).
PASSWORD()
does not perform
password encryption in the same way that Unix passwords are
encrypted. See ENCRYPT()
.
The PASSWORD()
function is
used by the authentication system in MySQL Server; you
should not use it in your own
applications. For that purpose, consider
MD5()
or
SHA1()
instead. Also see
RFC
2195, section 2 (Challenge-Response Authentication
Mechanism (CRAM)), for more information about
handling passwords and authentication securely in your
applications.
Calculates an SHA-1 160-bit checksum for the string, as
described in RFC 3174 (Secure Hash Algorithm). The value is
returned as a binary string of 40 hex digits, or
NULL
if the argument was
NULL
. One of the possible uses for this
function is as a hash key. You can also use it as a
cryptographic function for storing passwords.
SHA()
is
synonymous with SHA1()
.
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.
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
Name | Description |
---|---|
BENCHMARK() | Repeatedly execute an expression |
CHARSET() (v4.1.0) | Return the character set of the argument |
COERCIBILITY() (v4.1.1) | Return the collation coercibility value of the string argument |
COLLATION() (v4.1.0) | Return the collation of the string argument |
CONNECTION_ID() | Return the connection ID (thread ID) for the connection |
CURRENT_USER() , CURRENT_USER | Return the username and hostname combination |
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() (v5.0.1) | The number of rows updated |
SCHEMA() (v5.0.2) | A synonym for DATABASE() |
SESSION_USER() | Synonym for USER() |
SYSTEM_USER() | Synonym for USER() |
USER() | Return the current username and hostname |
VERSION() | Returns 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 always 0
. The intended
use is from within the mysql client,
which reports query execution times:
mysql> SELECT BENCHMARK(1000000,ENCODE('hello','goodbye'));
+----------------------------------------------+
| BENCHMARK(1000000,ENCODE('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
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 |
3 | System constant | USER() return value |
4 | Coercible | Literal string |
5 | Ignorable | NULL or an expression derived from
NULL |
Before MySQL 5.0.3, the return values are shown as follows,
and functions such as USER()
have a coercibility of 2:
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 | Coercible | Literal string |
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.
mysql> SELECT CONNECTION_ID();
-> 23786
Returns the username and hostname combination for the MySQL
account that the server used to authenticate the current
client. This account determines your access privileges. As
of MySQL 5.0.10, within a stored routine that is defined
with the SQL SECURITY DEFINER
characteristic,
CURRENT_USER()
returns the
creator of the routine. 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
username 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 username part
of the CURRENT_USER()
value). One way this might occur is that there is no account
listed in the grant tables for davida
.
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'
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 a 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 SELECT
statement, FOUND_ROWS()
returns the number of rows in the result set returned by
that statement.
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()
allows 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
.
FOUND_ROWS()
is not
replicated reliably, and should not be used with databases
that are to be replicated.
LAST_INSERT_ID()
,
LAST_INSERT_ID(
expr
)
LAST_INSERT_ID()
(with no
argument) returns the first
automatically generated value that was set for an
AUTO_INCREMENT
column by the
most recently executed
INSERT
statement to affect such a column.
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 will be 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;
Database changed mysql>CREATE TABLE t (
->id INT AUTO_INCREMENT NOT NULL PRIMARY KEY,
->name VARCHAR(10) NOT NULL
->);
Query OK, 0 rows affected (0.09 sec) mysql>INSERT INTO t VALUES (NULL, 'Bob');
Query OK, 1 row affected (0.01 sec) mysql>SELECT * FROM t;
+----+------+ | id | name | +----+------+ | 1 | Bob | +----+------+ 1 row in set (0.01 sec) mysql>SELECT LAST_INSERT_ID();
+------------------+ | LAST_INSERT_ID() | +------------------+ | 1 | +------------------+ 1 row in set (0.00 sec) mysql>INSERT INTO t VALUES
->(NULL, 'Mary'), (NULL, 'Jane'), (NULL, 'Lisa');
Query OK, 3 rows affected (0.00 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> SELECT * FROM t; +----+------+ | id | name | +----+------+ | 1 | Bob | | 2 | Mary | | 3 | Jane | | 4 | Lisa | +----+------+ 4 rows in set (0.01 sec) mysql>SELECT LAST_INSERT_ID();
+------------------+ | LAST_INSERT_ID() | +------------------+ | 2 | +------------------+ 1 row in set (0.00 sec)
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 AUTO_INCREMENT
counter is
not incremented and
LAST_INSERT_ID()
returns
0
, which reflects that no row was
inserted.
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 23.2.3.37, “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 the
number of rows updated, inserted, or deleted by the
preceding statement. This is the same as the row count that
the mysql client displays and the value
from the
mysql_affected_rows()
C API
function.
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()
was added in
MySQL 5.0.1.
ROW_COUNT()
is not
replicated reliably.
This function is a synonym for
DATABASE()
. It was added in
MySQL 5.0.2.
SESSION_USER()
is a synonym
for USER()
.
SYSTEM_USER()
is a synonym
for USER()
.
Returns the current MySQL username and hostname as a string
in the utf8
character set.
mysql> SELECT USER();
-> 'davida@localhost'
The value indicates the username 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()
.
You can extract only the username part like this:
mysql> SELECT SUBSTRING_INDEX(USER(),'@',1);
-> 'davida'
Returns a string that indicates the MySQL server version.
The string uses the utf8
character set.
mysql> SELECT VERSION();
-> '5.0.56-standard'
Note that if your version string ends with
-log
this means that logging is enabled.
Name | Description |
---|---|
DEFAULT() | Return the default value for a table column |
GET_LOCK() | Get a named lock |
INET_ATON() | Return the numeric value of an IP address |
INET_NTOA() | Return the IP address from a numeric value |
IS_FREE_LOCK() | Checks whether the named lock is free |
IS_USED_LOCK() (v4.1.0) | Checks whether the named lock is in use. Return connection identifier if true. |
MASTER_POS_WAIT() | Block until the slave has read and applied all updates up to the specified position |
NAME_CONST() (v5.0.12) | Causes the column to have the given name |
RAND() | Return a random floating-point value |
RELEASE_LOCK() | Releases the named lock |
SLEEP() (v5.0.12) | Sleep for a number of seconds |
UUID() (v4.1.2) | Return a Universal Unique Identifier (UUID) |
VALUES() (v4.1.1) | Defines the values to be used during an INSERT |
Returns the default value for a table column. Starting with MySQL 5.0.2, an error results if the column has no default value.
mysql> UPDATE t SET i = DEFAULT(i)+1 WHERE id < 100;
Formats the number X
to a format
like '#,###,###.##'
, rounded to
D
decimal places, and returns the
result as a string. For details, see
Section 11.4, “String Functions”.
Tries to obtain a lock with a name given by the string
str
, using a timeout of
timeout
seconds. 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). If you have a lock
obtained with GET_LOCK()
, it
is released when you execute
RELEASE_LOCK()
, execute a
new GET_LOCK()
, or your
connection terminates (either normally or abnormally). Locks
obtained with GET_LOCK()
do
not interact with transactions. That is, committing a
transaction does not release any such locks obtained during
the transaction.
This function 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 by one client,
GET_LOCK()
blocks any
request by another client for a lock with the same name.
This allows clients that agree on a given lock name to use
the name to perform cooperative advisory locking. But be
aware that it also allows 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
.
mysql>SELECT GET_LOCK('lock1',10);
-> 1 mysql>SELECT IS_FREE_LOCK('lock2');
-> 1 mysql>SELECT GET_LOCK('lock2',10);
-> 1 mysql>SELECT RELEASE_LOCK('lock2');
-> 1 mysql>SELECT RELEASE_LOCK('lock1');
-> NULL
The second RELEASE_LOCK()
call returns NULL
because the lock
'lock1'
was automatically released by the
second GET_LOCK()
call.
Note: If a client attempts to acquire a lock that is already
held by another client, it blocks according to the
timeout
argument. If the blocked
client terminates, its thread does not die until the lock
request times out. This is a known bug.
Given the dotted-quad representation of a network address as a string, returns an integer that represents the numeric value of the address. Addresses may be 4- or 8-byte addresses.
mysql> SELECT INET_ATON('209.207.224.40');
-> 3520061480
The generated number is always in network byte order. For the example just shown, the number is calculated as 209×2563 + 207×2562 + 224×256 + 40.
INET_ATON()
also understands
short-form IP addresses:
mysql> SELECT INET_ATON('127.0.0.1'), INET_ATON('127.1');
-> 2130706433, 2130706433
When storing values generated by
INET_ATON()
, it is
recommended that you use an INT
UNSIGNED
column. If you use a (signed)
INT
column, values corresponding to IP
addresses for which the first octet is greater than 127
cannot be stored correctly. See
Section 10.2, “Numeric Types”.
Given a numeric network address (4 or 8 byte), returns the dotted-quad representation of the address as a string.
mysql> SELECT INET_NTOA(3520061480);
-> '209.207.224.40'
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).
Checks whether the lock named str
is in use (that is, locked). If so, it returns the
connection identifier of the client that holds the lock.
Otherwise, it returns NULL
.
MASTER_POS_WAIT(
log_name
,log_pos
[,timeout
])
This function is useful for control of master/slave
synchronization. It blocks until the slave has read and
applied all updates up to the specified position in the
master log. The return value is the number of log events the
slave had to wait for to advance to the specified position.
The function returns NULL
if the slave
SQL thread is not started, the slave's master information is
not initialized, the arguments are incorrect, or an error
occurs. It returns -1
if the timeout has
been exceeded. If the slave SQL thread stops while
MASTER_POS_WAIT()
is
waiting, the function returns NULL
. If
the slave is past the specified position, the function
returns immediately.
If a timeout
value is specified,
MASTER_POS_WAIT()
stops
waiting when timeout
seconds have
elapsed. timeout
must be greater
than 0; a zero or negative
timeout
means no timeout.
Returns the given value. When used to produce a result set
column, NAME_CONST()
causes
the column to have the given name. The arguments should be
constants.
mysql> SELECT NAME_CONST('myname', 14);
+--------+
| myname |
+--------+
| 14 |
+--------+
This function was added in MySQL 5.0.12. It is for internal use only. The server uses it when writing statements from stored routines that contain references to local routine variables, as described in Section 18.5, “Binary Logging of Stored Routines and Triggers”, You might see this function in the output from mysqlbinlog.
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 12.2.2, “DO
Syntax”.
Sleeps (pauses) for the number of seconds given by the
duration
argument, then returns
0. If SLEEP()
is
interrupted, it returns 1. The duration may have a
fractional part given in microseconds. This function was
added in MySQL 5.0.12.
Returns a Universal Unique Identifier (UUID) generated according to “DCE 1.1: Remote Procedure Call” (Appendix A) CAE (Common Applications Environment) Specifications published by The Open Group in October 1997 (Document Number C706, http://www.opengroup.org/public/pubs/catalog/c706.htm).
A UUID is designed as a number that is globally unique in
space and time. Two calls to
UUID()
are expected to
generate two different values, even if these calls are
performed on two separate computers that are not connected
to each other.
A UUID is a 128-bit number represented by a
utf8
string of five hexadecimal numbers
in aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee
format:
The first three numbers are generated from a timestamp.
The fourth number preserves temporal uniqueness in case the timestamp value loses monotonicity (for example, due to daylight saving time).
The fifth number is an IEEE 802 node number that provides spatial uniqueness. A random number is substituted if the latter is not available (for example, because the host computer has no Ethernet card, or we do not know how to find the hardware address of an interface on your operating system). In this case, spatial uniqueness cannot be guaranteed. Nevertheless, a collision should have very low probability.
Currently, the MAC address of an interface is taken into account only on FreeBSD and Linux. On other operating systems, MySQL uses a randomly generated 48-bit number.
mysql> SELECT UUID();
-> '6ccd780c-baba-1026-9564-0040f4311e29'
Note that UUID()
does not
yet work with replication.
In an INSERT ... ON DUPLICATE KEY UPDATE
statement, you can use the
VALUES(
function in the col_name
)UPDATE
clause to refer to
column values from the INSERT
portion of
the statement. In other words,
VALUES(
in the col_name
)UPDATE
clause refers to the value
of col_name
that would be
inserted, had no duplicate-key conflict occurred. This
function is especially useful in multiple-row inserts. The
VALUES()
function is
meaningful only in INSERT ... ON DUPLICATE KEY
UPDATE
statements and returns
NULL
otherwise.
Section 12.2.4.3, “INSERT ... ON DUPLICATE KEY UPDATE
Syntax”.
mysql>INSERT INTO table (a,b,c) VALUES (1,2,3),(4,5,6)
->ON DUPLICATE KEY UPDATE c=VALUES(a)+VALUES(b);
Name | Description |
---|---|
AVG() | Return the average value of the argument |
BIT_AND() | Return bitwise and |
BIT_OR() | Return bitwise or |
BIT_XOR() (v4.1.1) | Return bitwise xor |
COUNT(DISTINCT) | Return the count of a number of different values |
COUNT() | Return a count of the number of rows returned |
GROUP_CONCAT() (v4.1) | Return a concatenated string |
MAX() | Return the maximum value |
MIN() | Return the minimum value |
STD() | Return the population standard deviation |
STDDEV_POP() (v5.0.3) | Return the population standard deviation |
STDDEV_SAMP() (v5.0.3) | Return the sample standard deviation |
STDDEV() | Return the population standard deviation |
SUM() | Return the sum |
VAR_POP() (v5.0.3) | Return the population standard variance |
VAR_SAMP() (v5.0.3) | Return the sample variance |
VARIANCE() (v4.1) | Return the population standard variance |
This section describes group (aggregate) functions that operate
on sets of values. Unless otherwise stated, group functions
ignore NULL
values.
If you use a group function in a statement containing no
GROUP BY
clause, it is equivalent to grouping
on all rows.
For numeric arguments, the variance and standard deviation
functions return a DOUBLE
value. The
SUM()
and
AVG()
functions return a
DECIMAL
value for exact-value arguments
(integer or DECIMAL
), and a
DOUBLE
value for approximate-value arguments
(FLOAT
or DOUBLE
). (Before
MySQL 5.0.3, SUM()
and
AVG()
return
DOUBLE
for all numeric arguments.)
The SUM()
and
AVG()
aggregate functions do not
work with temporal values. (They convert the values to numbers,
losing everything after the first non-numeric character.) To
work around this problem, you can convert to numeric units,
perform the aggregate operation, and convert back to a temporal
value. Examples:
SELECT SEC_TO_TIME(SUM(TIME_TO_SEC(time_col
))) FROMtbl_name
; SELECT FROM_DAYS(SUM(TO_DAYS(date_col
))) FROMtbl_name
;
Functions such as SUM()
or
AVG()
that expect a numeric
argument cast the argument to a number if necessary. For
SET
or ENUM
values, the
cast operation causes the underlying numeric value to be used.
Returns the average value of
. The
expr
DISTINCT
option can be used as of MySQL
5.0.3 to return the average of the distinct values of
expr
.
AVG()
returns
NULL
if there were no matching rows.
mysql>SELECT student_name, AVG(test_score)
->FROM student
->GROUP BY student_name;
Returns the bitwise AND
of all bits in
expr
. The calculation is
performed with 64-bit (BIGINT
) precision.
This function returns
18446744073709551615
if there were no
matching rows. (This is the value of an unsigned
BIGINT
value with all bits set to 1.)
Returns the bitwise OR
of all bits in
expr
. The calculation is
performed with 64-bit (BIGINT
) precision.
This function returns 0
if there were no
matching rows.
Returns the bitwise XOR
of
all bits in expr
. The calculation
is performed with 64-bit (BIGINT
)
precision.
This function returns 0
if there were no
matching rows.
Returns a count of the number of non-NULL
values of expr
in the rows
retrieved by a SELECT
statement. The
result is a BIGINT
value.
COUNT()
returns
0
if there were no matching rows.
mysql>SELECT student.student_name,COUNT(*)
->FROM student,course
->WHERE student.student_id=course.student_id
->GROUP BY student_name;
COUNT(*)
is somewhat
different in that it returns a count of the number of rows
retrieved, whether or not they contain
NULL
values.
COUNT(*)
is optimized to
return very quickly if the SELECT
retrieves from one table, no other columns are retrieved,
and there is no WHERE
clause. For
example:
mysql> SELECT COUNT(*) FROM student;
This optimization applies only to MyISAM
tables only, because an exact row count is stored for this
storage engine and can be accessed very quickly. For
transactional storage engines such as
InnoDB
and BDB
,
storing an exact row count is more problematic because
multiple transactions may be occurring, each of which may
affect the count.
COUNT(DISTINCT
expr
,[expr
...])
Returns a count of the number of different
non-NULL
values.
COUNT(DISTINCT)
returns
0
if there were no matching rows.
mysql> SELECT COUNT(DISTINCT results) FROM student;
In MySQL, you can obtain the number of distinct expression
combinations that do not contain NULL
by
giving a list of expressions. In standard SQL, you would
have to do a concatenation of all expressions inside
COUNT(DISTINCT ...)
.
This function returns a string result with the concatenated
non-NULL
values from a group. It returns
NULL
if there are no
non-NULL
values. The full syntax is as
follows:
GROUP_CONCAT([DISTINCT]expr
[,expr
...] [ORDER BY {unsigned_integer
|col_name
|expr
} [ASC | DESC] [,col_name
...]] [SEPARATORstr_val
])
mysql>SELECT student_name,
->GROUP_CONCAT(test_score)
->FROM student
->GROUP BY student_name;
Or:
mysql>SELECT student_name,
->GROUP_CONCAT(DISTINCT test_score
->ORDER BY test_score DESC SEPARATOR ' ')
->FROM student
->GROUP BY student_name;
In MySQL, you can get the concatenated values of expression
combinations. You can eliminate duplicate values by using
DISTINCT
. If you want to sort values in
the result, you should use ORDER BY
clause. To sort in reverse order, add the
DESC
(descending) keyword to the name of
the column you are sorting by in the ORDER
BY
clause. The default is ascending order; this
may be specified explicitly using the ASC
keyword. SEPARATOR
is followed by the
string value that should be inserted between values of
result. The default is a comma
(“,
”). You can eliminate the
separator altogether by specifying SEPARATOR
''
.
The result is truncated to the maximum length that is given
by the group_concat_max_len
system
variable, which has a default value of 1024. The value can
be set higher, although the effective maximum length of the
return value is constrained by the value of
max_allowed_packet
. The syntax to change
the value of group_concat_max_len
at
runtime is as follows, where val
is an unsigned integer:
SET [SESSION | GLOBAL] group_concat_max_len = val
;
Beginning with MySQL 5.0.19, the type returned by
GROUP_CONCAT()
is always
VARCHAR
unless
group_concat_max_len
is greater than 512,
in which case, it returns a BLOB
.
(Previously, it returned a BLOB
with
group_concat_max_len
greater than 512
only if the query included an ORDER BY
clause.)
See also CONCAT()
and
CONCAT_WS()
:
Section 11.4, “String Functions”.
Returns the maximum value of
expr
.
MAX()
may take a string
argument; in such cases, it returns the maximum string
value. See Section 7.4.5, “How MySQL Uses Indexes”. The
DISTINCT
keyword can be used to find the
maximum of the distinct values of
expr
, however, this produces the
same result as omitting DISTINCT
.
MAX()
returns
NULL
if there were no matching rows.
mysql>SELECT student_name, MIN(test_score), MAX(test_score)
->FROM student
->GROUP BY student_name;
For MAX()
, MySQL currently
compares ENUM
and SET
columns by their string value rather than by the string's
relative position in the set. This differs from how
ORDER BY
compares them. This is expected
to be rectified in a future MySQL release.
Returns the minimum value of
expr
.
MIN()
may take a string
argument; in such cases, it returns the minimum string
value. See Section 7.4.5, “How MySQL Uses Indexes”. The
DISTINCT
keyword can be used to find the
minimum of the distinct values of
expr
, however, this produces the
same result as omitting DISTINCT
.
MIN()
returns
NULL
if there were no matching rows.
mysql>SELECT student_name, MIN(test_score), MAX(test_score)
->FROM student
->GROUP BY student_name;
For MIN()
, MySQL currently
compares ENUM
and SET
columns by their string value rather than by the string's
relative position in the set. This differs from how
ORDER BY
compares them. This is expected
to be rectified in a future MySQL release.
Returns the population standard deviation of
expr
. This is an extension to
standard SQL. As of MySQL 5.0.3, the standard SQL function
STDDEV_POP()
can be used
instead.
This function returns NULL
if there were
no matching rows.
Returns the population standard deviation of
expr
. This function is provided
for compatibility with Oracle. As of MySQL 5.0.3, the
standard SQL function
STDDEV_POP()
can be used
instead.
This function returns NULL
if there were
no matching rows.
Returns the population standard deviation of
expr
(the square root of
VAR_POP()
). This function
was added in MySQL 5.0.3. Before 5.0.3, you can use
STD()
or
STDDEV()
, which are
equivalent but not standard SQL.
STDDEV_POP()
returns
NULL
if there were no matching rows.
Returns the sample standard deviation of
expr
(the square root of
VAR_SAMP()
. This function
was added in MySQL 5.0.3.
STDDEV_SAMP()
returns
NULL
if there were no matching rows.
Returns the sum of expr
. If the
return set has no rows,
SUM()
returns
NULL
. The DISTINCT
keyword can be used in MySQL 5.0 to sum only
the distinct values of expr
.
SUM()
returns
NULL
if there were no matching rows.
Returns the population standard variance of
expr
. It considers rows as the
whole population, not as a sample, so it has the number of
rows as the denominator. This function was added in MySQL
5.0.3. Before 5.0.3, you can use
VARIANCE()
, which is
equivalent but is not standard SQL.
VAR_POP()
returns
NULL
if there were no matching rows.
Returns the sample variance of
expr
. That is, the denominator is
the number of rows minus one. This function was added in
MySQL 5.0.3.
VAR_SAMP()
returns
NULL
if there were no matching rows.
Returns the population standard variance of
expr
. This is an extension to
standard SQL. As of MySQL 5.0.3, the standard SQL function
VAR_POP()
can be used
instead.
VARIANCE()
returns
NULL
if there were no matching rows.
The GROUP BY
clause allows a WITH
ROLLUP
modifier that causes extra rows to be added to
the summary output. These rows represent higher-level (or
super-aggregate) summary operations. ROLLUP
thus allows you to answer questions at multiple levels of
analysis with a single query. It can be used, for example, to
provide support for OLAP (Online Analytical Processing)
operations.
Suppose that a table named sales
has
year
, country
,
product
, and profit
columns for recording sales profitability:
CREATE TABLE sales ( year INT NOT NULL, country VARCHAR(20) NOT NULL, product VARCHAR(32) NOT NULL, profit INT );
The table's contents can be summarized per year with a simple
GROUP BY
like this:
mysql> SELECT year, SUM(profit) FROM sales GROUP BY year;
+------+-------------+
| year | SUM(profit) |
+------+-------------+
| 2000 | 4525 |
| 2001 | 3010 |
+------+-------------+
This output shows the total profit for each year, but if you also want to determine the total profit summed over all years, you must add up the individual values yourself or run an additional query.
Or you can use ROLLUP
, which provides both
levels of analysis with a single query. Adding a WITH
ROLLUP
modifier to the GROUP BY
clause causes the query to produce another row that shows the
grand total over all year values:
mysql> SELECT year, SUM(profit) FROM sales GROUP BY year WITH ROLLUP;
+------+-------------+
| year | SUM(profit) |
+------+-------------+
| 2000 | 4525 |
| 2001 | 3010 |
| NULL | 7535 |
+------+-------------+
The grand total super-aggregate line is identified by the value
NULL
in the year
column.
ROLLUP
has a more complex effect when there
are multiple GROUP BY
columns. In this case,
each time there is a “break” (change in value) in
any but the last grouping column, the query produces an extra
super-aggregate summary row.
For example, without ROLLUP
, a summary on the
sales
table based on year
,
country
, and product
might
look like this:
mysql>SELECT year, country, product, SUM(profit)
->FROM sales
->GROUP BY year, country, product;
+------+---------+------------+-------------+ | year | country | product | SUM(profit) | +------+---------+------------+-------------+ | 2000 | Finland | Computer | 1500 | | 2000 | Finland | Phone | 100 | | 2000 | India | Calculator | 150 | | 2000 | India | Computer | 1200 | | 2000 | USA | Calculator | 75 | | 2000 | USA | Computer | 1500 | | 2001 | Finland | Phone | 10 | | 2001 | USA | Calculator | 50 | | 2001 | USA | Computer | 2700 | | 2001 | USA | TV | 250 | +------+---------+------------+-------------+
The output indicates summary values only at the
year/country/product level of analysis. When
ROLLUP
is added, the query produces several
extra rows:
mysql>SELECT year, country, product, SUM(profit)
->FROM sales
->GROUP BY year, country, product WITH ROLLUP;
+------+---------+------------+-------------+ | year | country | product | SUM(profit) | +------+---------+------------+-------------+ | 2000 | Finland | Computer | 1500 | | 2000 | Finland | Phone | 100 | | 2000 | Finland | NULL | 1600 | | 2000 | India | Calculator | 150 | | 2000 | India | Computer | 1200 | | 2000 | India | NULL | 1350 | | 2000 | USA | Calculator | 75 | | 2000 | USA | Computer | 1500 | | 2000 | USA | NULL | 1575 | | 2000 | NULL | NULL | 4525 | | 2001 | Finland | Phone | 10 | | 2001 | Finland | NULL | 10 | | 2001 | USA | Calculator | 50 | | 2001 | USA | Computer | 2700 | | 2001 | USA | TV | 250 | | 2001 | USA | NULL | 3000 | | 2001 | NULL | NULL | 3010 | | NULL | NULL | NULL | 7535 | +------+---------+------------+-------------+
For this query, adding ROLLUP
causes the
output to include summary information at four levels of
analysis, not just one. Here's how to interpret the
ROLLUP
output:
Following each set of product rows for a given year and
country, an extra summary row is produced showing the total
for all products. These rows have the
product
column set to
NULL
.
Following each set of rows for a given year, an extra
summary row is produced showing the total for all countries
and products. These rows have the country
and products
columns set to
NULL
.
Finally, following all other rows, an extra summary row is
produced showing the grand total for all years, countries,
and products. This row has the year
,
country
, and products
columns set to NULL
.
Other Considerations When using
ROLLUP
The following items list some behaviors specific to the MySQL
implementation of ROLLUP
:
When you use ROLLUP
, you cannot also use an
ORDER BY
clause to sort the results. In other
words, ROLLUP
and ORDER BY
are mutually exclusive. However, you still have some control
over sort order. GROUP BY
in MySQL sorts
results, and you can use explicit ASC
and
DESC
keywords with columns named in the
GROUP BY
list to specify sort order for
individual columns. (The higher-level summary rows added by
ROLLUP
still appear after the rows from which
they are calculated, regardless of the sort order.)
LIMIT
can be used to restrict the number of
rows returned to the client. LIMIT
is applied
after ROLLUP
, so the limit applies against
the extra rows added by ROLLUP
. For example:
mysql>SELECT year, country, product, SUM(profit)
->FROM sales
->GROUP BY year, country, product WITH ROLLUP
->LIMIT 5;
+------+---------+------------+-------------+ | year | country | product | SUM(profit) | +------+---------+------------+-------------+ | 2000 | Finland | Computer | 1500 | | 2000 | Finland | Phone | 100 | | 2000 | Finland | NULL | 1600 | | 2000 | India | Calculator | 150 | | 2000 | India | Computer | 1200 | +------+---------+------------+-------------+
Using LIMIT
with ROLLUP
may produce results that are more difficult to interpret,
because you have less context for understanding the
super-aggregate rows.
The NULL
indicators in each super-aggregate
row are produced when the row is sent to the client. The server
looks at the columns named in the GROUP BY
clause following the leftmost one that has changed value. For
any column in the result set with a name that is a lexical match
to any of those names, its value is set to
NULL
. (If you specify grouping columns by
column number, the server identifies which columns to set to
NULL
by number.)
Because the NULL
values in the
super-aggregate rows are placed into the result set at such a
late stage in query processing, you cannot test them as
NULL
values within the query itself. For
example, you cannot add HAVING product IS
NULL
to the query to eliminate from the output all but
the super-aggregate rows.
On the other hand, the NULL
values do appear
as NULL
on the client side and can be tested
as such using any MySQL client programming interface.
MySQL extends the use of GROUP BY
so that you
can use non-aggregated columns or calculations in the
SELECT
list that do not appear in the
GROUP BY
clause. You can use this feature to
get better performance by avoiding unnecessary column sorting
and grouping. For example, you do not need to group on
customer.name
in the following query:
SELECT order.custid, customer.name, MAX(payments) FROM order,customer WHERE order.custid = customer.custid GROUP BY order.custid;
In standard SQL, you would have to add
customer.name
to the GROUP
BY
clause. In MySQL, the name is redundant.
Do not use this feature if the columns you
omit from the GROUP BY
part are not constant
in the group. The server is free to return any value from the
group, so the results are indeterminate unless all values are
the same.
A similar MySQL extension applies to the
HAVING
clause. The SQL standard does not
allow the HAVING
clause to name any column
that is not found in the GROUP BY
clause if
it is not enclosed in an aggregate function. MySQL allows the
use of such columns to simplify calculations. This extension
assumes that the non-grouped columns will have the same
group-wise values. Otherwise, the result is indeterminate.
If the ONLY_FULL_GROUP_BY
SQL mode is
enabled, the MySQL extension to GROUP BY
does
not apply. That is, columns not named in the GROUP
BY
clause cannot be used in the
SELECT
list or HAVING
clause if not used in an aggregate function.
The select list extension also applies to ORDER
BY
. That is, you can use non-aggregated columns or
calculations in the ORDER BY
clause that do
not appear in the GROUP BY
clause. This
extension does not apply if the
ONLY_FULL_GROUP_BY
SQL mode is enabled.
In some cases, you can use MIN()
and MAX()
to obtain a specific
column value even if it isn't unique. The following gives the
value of column
from the row containing the
smallest value in the sort
column:
SUBSTR(MIN(CONCAT(RPAD(sort,6,' '),column)),7)
See Section 3.6.4, “The Rows Holding the Group-wise Maximum of a Certain Field”.
Note that if you are trying to follow standard SQL, you can't
use expressions in GROUP BY
clauses. You can
work around this limitation by using an alias for the
expression:
SELECT id,FLOOR(value/100) AS val
FROM tbl_name
GROUP BY id, val;
MySQL does allow expressions in GROUP BY
clauses. For example:
SELECT id,FLOOR(value/100)
FROM tbl_name
GROUP BY id, FLOOR(value/100);