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12 Functions and Operators

A select_expression or where_definition in an SQL statement can consist of any expression using the functions described below.

An expression that contains NULL always produces a NULL value unless otherwise indicated in the documentation for the operators and functions involved in the expression.

Note: There must be no whitespace between a function name and the parentheses 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. Spaces around arguments are permitted, though.

You can force MySQL to accept spaces after the function name by starting mysqld with --ansi or using the CLIENT_IGNORE_SPACE to mysql_connect(), but in this case, all function names will become reserved words. See section 1.8.3 Running MySQL in ANSI Mode.

For the sake of brevity, examples display the output from the mysql program in abbreviated form. So this:

mysql> SELECT MOD(29,9);
1 rows in set (0.00 sec)

+-----------+
| mod(29,9) |
+-----------+
|         2 |
+-----------+

is displayed like this:

mysql> SELECT MOD(29,9);
        -> 2

12.1 Non-Type-Specific Operators and Functions

12.1.1 Parentheses

( ... )

Use parentheses to force the order of evaluation in an expression. For example:

mysql> SELECT 1+2*3;
        -> 7
mysql> SELECT (1+2)*3;
        -> 9

12.1.2 Comparison Operators

Comparison operations result in a value of 1 (TRUE), 0 (FALSE), or NULL. These functions work for both numbers and strings. Strings are automatically converted to numbers and numbers to strings as needed (as in Perl).

MySQL performs comparisons using the following rules:

By default, string comparisons are done in case-independent fashion using the current character set (ISO-8859-1 Latin1 by default, which also works excellently for English).

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 can't use index to quickly look up the value:

SELECT * FROM table_name WHERE string_key=1

The reason for this is that there is many different strings that may return the value 1: "1", " 1", "1a" ...

=
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
<>
!=
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
<=>
NULL-safe equal:
mysql> SELECT 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
        -> 1 1 0
IS NULL
IS NOT NULL
Test whether a value is or is not NULL:
mysql> SELECT 1 IS NULL, 0 IS NULL, NULL IS NULL;
        -> 0 0 1
mysql> SELECT 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL;
        -> 1 1 0
To be able to work well with other programs, MySQL supports the following extra features when using IS NULL:
expr BETWEEN min AND max
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 (min <= expr AND expr <= max) if all the arguments are of the same type. Otherwise type conversion takes place, according to the rules above, but applied to all the three arguments. Note that before 4.0.5 arguments were converted to the type of expr instead.
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
expr NOT BETWEEN min AND max
Same as NOT (expr BETWEEN min AND max).
expr IN (value,...)
Returns 1 if expr is any of the values in the IN list, else returns 0. If all values are constants, then all values are evaluated according to the type of expr and sorted. The search for the item is then done using a binary search. This means IN is very quick if the IN value list consists entirely of constants. If expr is a case-sensitive string expression, the string comparison is performed in case-sensitive fashion:
mysql> SELECT 2 IN (0,3,5,'wefwf');
        -> 0
mysql> SELECT 'wefwf' IN (0,3,5,'wefwf');
        -> 1
The number of values in the IN list is only limited by the max_allowed_packet value. From 4.1 (to comply with the SQL-99 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. From MySQL version 4.1, an IN() clause may also contain a subquery. See section 13.1.8.3 Subqueries with ANY, IN, and SOME.
expr NOT IN (value,...)
Same as NOT (expr IN (value,...)).
ISNULL(expr)
If expr is NULL, ISNULL() returns 1, otherwise it returns 0:
mysql> SELECT ISNULL(1+1);
        -> 0
mysql> SELECT ISNULL(1/0);
        -> 1
Note that a comparison of NULL values using = will always be false!
COALESCE(list)
Returns first non-NULL element in list:
mysql> SELECT COALESCE(NULL,1);
        -> 1
mysql> SELECT COALESCE(NULL,NULL,NULL);
        -> NULL
INTERVAL(N,N1,N2,N3,...)
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

12.1.3 Logical Operators

In SQL, all logical operators evaluate to TRUE, FALSE or NULL (UNKNOWN). In MySQL, this is implemented as 1 (TRUE), 0 (FALSE), and NULL. Most of this is common between different SQL databases, however some may return any non-zero value for TRUE.

NOT
!
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.
AND
&&
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
Please note that MySQL versions prior to 4.0.5 stop evaluation when a NULL is encountered, rather than continuing the process to check for possible 0 values. This means that in these versions, SELECT (NULL AND 0) returns NULL instead of 0. In 4.0.5 the code has been re-engineered so that the result will always be as prescribed by the SQL standards while still using the optimization wherever possible.
OR
||
Logical OR. Evaluates to 1 if any operand is non-zero, to NULL if any operand is NULL, otherwise 0 is returned.
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
XOR
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). XOR was added in version 4.0.2.

12.1.4 Control Flow Functions

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 value=compare-value. The second version returns the result for the first condition, which is true. If there was no matching result value, then the result after ELSE is returned. If there is no ELSE part then NULL is returned:
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 type of the return value (INTEGER, DOUBLE or STRING) is the same as the type of the first returned value (the expression after the first THEN).
IF(expr1,expr2,expr3)
If expr1 is TRUE (expr1 <> 0 and expr1 <> NULL) then IF() returns expr2, else 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 expr2 or expr3 is explicitly NULL then the result type of the IF() function is the type of the not NULL column. (This behavior is new in MySQL 4.0.3). 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 above, 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 in MySQL Version 3.23 as follows:
Expression Return value
expr2 or expr3 returns string string
expr2 or expr3 returns a floating-point value floating-point
expr2 or expr3 returns an integer integer
If expr2 and expr3 are strings, then the result is case insensitive if both strings are case-insensitive. (Starting from 3.23.51)
IFNULL(expr1,expr2)
If expr1 is not NULL, IFNULL() returns expr1, else 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'
In MySQL 4.0.6 and above, the default result value of IFNULL(expr1,expr2) is the more ``general'' of the two expressions, in the order STRING, REAL or INTEGER. The difference to earlier MySQL versions are mostly notable when you create a table based on expressions or MySQL has to internally store a value from IFNULL() in a temporary table.
CREATE TABLE foo SELECT IFNULL(1,"test") as test;
In MySQL 4.0.6, the type for column 'test' is CHAR(4) while in earlier versions you would get BIGINT.
NULLIF(expr1,expr2)
If expr1 = expr2 is true, return NULL else return expr1. This is the same as CASE WHEN x = y THEN NULL ELSE x END:
mysql> SELECT NULLIF(1,1);
        -> NULL
mysql> SELECT NULLIF(1,2);
        -> 1
Note that expr1 is evaluated twice in MySQL if the arguments are not equal.

12.2 String Functions

String-valued functions return NULL if the length of the result would be greater than the max_allowed_packet server parameter. See section 7.5.2 Tuning Server Parameters.

For functions that operate on string positions, the first position is numbered 1.

ASCII(str)
Returns the ASCII code value of the leftmost character of the string str. Returns 0 if str is the empty string. Returns NULL if str is NULL:
mysql> SELECT ASCII('2');
        -> 50
mysql> SELECT ASCII(2);
        -> 50
mysql> SELECT ASCII('dx');
        -> 100
See also the ORD() function.
BIN(N)
Returns a string representation of the binary value of N, where N is a longlong (BIGINT) number. This is equivalent to CONV(N,10,2). Returns NULL if N is NULL:
mysql> SELECT BIN(12);
        -> '1100'
BIT_LENGTH(str)
Returns the length of the string str in bits:
mysql> SELECT BIT_LENGTH('text');
        -> 32
CHAR(N,...)
CHAR() interprets the arguments as integers and returns a string consisting of the characters given by the ASCII code values of those integers. NULL values are skipped:
mysql> SELECT CHAR(77,121,83,81,'76');
        -> 'MySQL'
mysql> SELECT CHAR(77,77.3,'77.3');
        -> 'MMM'
CHAR_LENGTH(str)
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(str)
CHARACTER_LENGTH() is a synonym for CHAR_LENGTH().
COMPRESS(string_to_compress)
Compresses a string.
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
COMPRESS() was added in MySQL version 4.1.1. It requires MySQL to have been compiled with a compression library such as zlib. Otherwise, the return value is always NULL. The compressed string contents are stored the following way:
CONCAT(str1,str2,...)
Returns the string that results from concatenating the arguments. Returns NULL if any argument is NULL. May have more than two arguments. A numeric argument is converted to its equivalent string form:
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 CONCAT 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. The function skips any NULL values after the separator argument.
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'
Before MySQL 4.0.14, CONCAT_WS() skips empty strings as well as NULL values.
CONV(N,from_base,to_base)
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'
ELT(N,str1,str2,str3,...)
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 in which for every bit set in bits, you get an on string and for every reset bit you get an off string. Each string is separated by separator (default ,), and only number_of_bits (default 64) of bits is used:
mysql> SELECT EXPORT_SET(5,'Y','N',',',4)
        -> Y,N,Y,N
FIELD(str,str1,str2,str3,...)
Returns the index of str in the str1, str2, str3, ... list. Returns 0 if str is not found. 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
FIND_IN_SET(str,strlist)
Returns a value 1 to N if the string str is in the 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 will not work properly if the first argument contains a comma `,':
mysql> SELECT FIND_IN_SET('b','a,b,c,d');
        -> 2
HEX(N_or_S)
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 of N_OR_S where each character in N_OR_S is converted to two hexadecimal digits.
mysql> SELECT HEX(255);
        -> 'FF'
mysql> SELECT HEX("abc");
        -> 616263
mysql> SELECT 0x616263;
        -> "abc"
INSERT(str,pos,len,newstr)
Returns the string str, with the substring beginning at position pos and len characters long replaced by the string newstr:
mysql> SELECT INSERT('Quadratic', 3, 4, 'What');
        -> 'QuWhattic'
This function is multi-byte safe.
INSTR(str,substr)
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 arguments are swapped:
mysql> SELECT INSTR('foobarbar', 'bar');
        -> 4
mysql> SELECT INSTR('xbar', 'foobar');
        -> 0
This function is multi-byte safe. In MySQL 3.23 this function is case sensitive, while in 4.0 it's only case sensitive if either argument is a binary string.
LCASE(str)
LCASE() is a synonym for LOWER().
LEFT(str,len)
Returns the leftmost len characters from the string str:
mysql> SELECT LEFT('foobarbar', 5);
        -> 'fooba'
LENGTH(str)
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
LOAD_FILE(file_name)
Reads the file and returns the file contents as a string. The file must be on the server, you must specify the full pathname to the file, and you must have the FILE privilege. The file must be readable by all and be smaller than max_allowed_packet. If the file doesn't exist or can't be read due to one of these reasons, the function returns NULL:
mysql> UPDATE tbl_name
           SET blob_column=LOAD_FILE("/tmp/picture")
           WHERE id=1;
If you are not using MySQL Version 3.23, you have to do the reading of the file inside your application and create an INSERT statement to update the database with the file information. One way to do this, if you are using the MySQL++ library, can be found at http://www.mysql.com/documentation/mysql++/mysql++-examples.html.
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. In MySQL 3.23 this function is case sensitive, while in 4.0 it's only case sensitive if either argument is a binary string.
LOWER(str)
Returns the string str with all characters changed to lowercase according to the current character set mapping (the default is ISO-8859-1 Latin1):
mysql> SELECT LOWER('QUADRATICALLY');
        -> 'quadratically'
This function is multi-byte safe.
LPAD(str,len,padstr)
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'
LTRIM(str)
Returns the string str with leading space characters removed:
mysql> SELECT LTRIM('  barbar');
        -> 'barbar'
MAKE_SET(bits,str1,str2,...)
Returns a set (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, etc. NULL strings 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(0,'a','b','c');
        -> ''
MID(str,pos,len)
MID(str,pos,len) is a synonym for SUBSTRING(str,pos,len).
OCT(N)
Returns a string representation of the octal value of N, where N is a longlong number. This is equivalent to CONV(N,10,8). Returns NULL if N is NULL:
mysql> SELECT OCT(12);
        -> '14'
OCTET_LENGTH(str)
OCTET_LENGTH() is a synonym for LENGTH().
ORD(str)
If the leftmost character of the string str is a multi-byte character, returns the code for that character, calculated from the ASCII code values of its constituent characters using this formula: ((first byte ASCII code)*256+(second byte ASCII code))[*256+third byte ASCII code...]. If the leftmost character is not a multi-byte character, returns the same value that the ASCII() function does:
mysql> SELECT ORD('2');
        -> 50
POSITION(substr IN str)
POSITION(substr IN str) is a synonym for LOCATE(substr,str).
QUOTE(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 surrounded 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 surrounding single quotes. The QUOTE() function was added in MySQL version 4.0.3.
mysql> SELECT QUOTE("Don't");
        -> 'Don\'t!'
mysql> SELECT QUOTE(NULL);
        -> NULL
REPEAT(str,count)
Returns a string consisting of the string str repeated count times. If count <= 0, returns an empty string. Returns NULL if str or count are NULL:
mysql> SELECT REPEAT('MySQL', 3);
        -> 'MySQLMySQLMySQL'
REPLACE(str,from_str,to_str)
Returns the string str with all occurrences of the string from_str replaced by the string to_str:
mysql> SELECT REPLACE('www.mysql.com', 'w', 'Ww');
        -> 'WwWwWw.mysql.com'
This function is multi-byte safe.
REVERSE(str)
Returns the string str with the order of the characters reversed:
mysql> SELECT REVERSE('abc');
        -> 'cba'
This function is multi-byte safe.
RIGHT(str,len)
Returns the rightmost len characters from the string str:
mysql> SELECT RIGHT('foobarbar', 4);
        -> 'rbar'
This function is multi-byte safe.
RPAD(str,len,padstr)
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???'
This function is multi-byte safe.
RTRIM(str)
Returns the string str with trailing space characters removed:
mysql> SELECT RTRIM('barbar   ');
        -> 'barbar'
This function is multi-byte safe.
SOUNDEX(str)
Returns a soundex string from str. Two strings that sound almost the same should have identical soundex strings. A standard soundex string is 4 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-alphanumeric characters are ignored in the given string. All international alpha characters outside the A-Z range are treated as vowels:
mysql> SELECT SOUNDEX('Hello');
        -> 'H400'
mysql> SELECT SOUNDEX('Quadratically');
        -> 'Q36324'
Note: this function implements the original Soundex algorithm, not the more popular enhanced version (also described by D. Knuth). The difference is that original version first discards vowels, and then - duplicates, while the enhanced removes duplicates first.
expr1 SOUNDS LIKE expr2
Same as SOUNDEX(expr1)=SOUNDEX(expr2) (available only in version 4.1 or later).
SPACE(N)
Returns a string consisting of N space characters:
mysql> SELECT SPACE(6);
        -> '      '
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 SQL-92 syntax.
mysql> SELECT SUBSTRING('Quadratically',5);
        -> 'ratically'
mysql> SELECT SUBSTRING('foobarbar' FROM 4);
        -> 'barbar'
mysql> SELECT SUBSTRING('Quadratically',5,6);
        -> 'ratica'
This function is multi-byte safe.
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:
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)
Returns the string str with all remstr prefixes and/or suffixes removed. If none of the specifiers BOTH, LEADING or TRAILING is given, BOTH is assumed. If remstr is 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.
UCASE(str)
UCASE() is a synonym for UPPER().
UNCOMPRESS(string_to_uncompress)
Uncompresses a string compressed by the COMPRESS() function.
mysql> SELECT UNCOMPRESS(COMPRESS("any string"));
        -> 'any string'
UNCOMPRESS() was added in MySQL version 4.1.1. It requires MySQL to have been compiled with a compression library such as zlib. Otherwise, the return value is always NULL.
UNCOMPRESSED_LENGTH(compressed_string)
Returns the length of a compressed string before compressing.
mysql> SELECT UNCOMPRESSED_LENGTH(COMPRESS(REPEAT("a",30)));
        -> 30
UNCOMPRESSED_LENGTH() was added in MySQL version 4.1.1.
UNHEX()
Does the opposite of HEX(string), that is returns a string where each byte is specified by a two hexadecimal digits in a string argument.
mysql> SELECT UNHEX("4D7953514C");
        -> "MySQL"
mysql> SELECT 0x4D7953514C;
        -> "MySQL"
mysql> SELECT UNHEX(HEX("string"));
        -> "string"
mysql> SELECT HEX(UNHEX("1267"));
        -> "1267"
UPPER(str)
Returns the string str with all characters changed to uppercase according to the current character set mapping (the default is ISO-8859-1 Latin1):
mysql> SELECT UPPER('Hej');
        -> 'HEJ'
This function is multi-byte safe.

12.2.1 String Comparison Functions

MySQL automatically converts numbers to strings as necessary, and vice-versa:

mysql> SELECT 1+"1";
        -> 2
mysql> SELECT CONCAT(2,' test');
        -> '2 test'

If you want to convert a number to a string explicitly, pass it as the argument to CONCAT().

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 only affects 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). With LIKE you can use the following two wildcard characters in the pattern:
Char 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 the character with the escape character. If you don't 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 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
LIKE is allowed on numeric expressions! (This is a MySQL extension to the SQL-99 LIKE.)
mysql> SELECT 10 LIKE '1%';
        -> 1
Note: Because MySQL uses the C escape syntax in strings (for example, `\n'), you must double any `\' that you use in your LIKE strings. For example, to search for `\n', specify it as `\\n'. To search for `\', specify it as `\\\\' (the backslashes are stripped once by the parser and another time when the pattern match is done, leaving a single backslash to be matched). Note: Currently LIKE is not multi-byte character safe. Comparison is done character by character.
MATCH (col1,col2,...) AGAINST (expr [IN BOOLEAN MODE | WITH QUERY EXPANSION] )
MATCH ... AGAINST() is used for full-text search and returns relevance - similarity measure between the text in columns (col1,col2,...) and the query expr. Relevance is a positive floating-point number. Zero relevance means no similarity. MATCH ... AGAINST() is available in MySQL version 3.23.23 or later. IN BOOLEAN MODE extension was added in version 4.0.1, WITH QUERY EXPANSION was added in 4.1.1. For details and usage examples, see section 13.7 MySQL Full-text Search.
expr NOT LIKE pat [ESCAPE 'escape-char']
Same as NOT (expr LIKE pat [ESCAPE 'escape-char']).
expr NOT REGEXP pat
expr NOT RLIKE pat
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. See section F MySQL Regular Expressions. Returns 1 if expr matches pat, otherwise returns 0. RLIKE is a synonym for REGEXP, provided for mSQL compatibility. Note: Because MySQL uses the C escape syntax in strings (for example, `\n'), you must double any `\' that you use in your REGEXP strings. As of MySQL Version 3.23.4, REGEXP is not case sensitive for normal (not 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 (ISO-8859-1 Latin1 by default) when deciding the type of a character.
STRCMP(expr1,expr2)
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
As of MySQL 4.0, 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. Before MySQL 4.0, STRCMP() is case sensitive.

12.2.2 Case-Sensitivity

BINARY
The BINARY operator casts the string following it to a binary string. This is an easy way to force a column comparison to be case sensitive even if the column isn't defined as BINARY or BLOB:
mysql> SELECT "a" = "A";
        -> 1
mysql> SELECT BINARY "a" = "A";
        -> 0
BINARY string is a shorthand for CAST(string AS BINARY). See section 12.5 Cast Functions. BINARY was introduced in MySQL Version 3.23.0. Note that in some contexts, if you cast an indexed column to BINARY, MySQL will not be able to use the index efficiently.

If you want to compare a BLOB value in case-insensitive fashion, you can do so as follows:

CONVERT() can be used more generally for comparing strings that are represented in different character sets.

12.3 Numeric Functions

12.3.1 Arithmetic Operations

The usual arithmetic operators are available. Note that in the case of `-', `+', and `*', the result is calculated with BIGINT (64-bit) precision if both arguments are integers! If one of the argument is an unsigned integer, and the other argument is also an integer, the result will be an unsigned integer. See section 12.5 Cast Functions.

+
Addition:
mysql> SELECT 3+5;
        -> 8
-
Subtraction:
mysql> SELECT 3-5;
        -> -2
*
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.
/
Division:
mysql> SELECT 3/5;
        -> 0.60
Division by zero produces a NULL result:
mysql> SELECT 102/(1-1);
        -> NULL
A division will be calculated with BIGINT arithmetic only if performed in a context where its result is converted to an integer!

12.3.2 Mathematical Functions

All mathematical functions return NULL in case of an error.

-
Unary minus. Changes the sign of the argument:
mysql> SELECT - 2;
        -> -2
Note that if this operator is used with a BIGINT, the return value is a BIGINT! This means that you should avoid using - on integers that may have the value of -2^63!
ABS(X)
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.
ACOS(X)
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);
        -> 0.000000
mysql> SELECT ACOS(1.0001);
        -> NULL
mysql> SELECT ACOS(0);
        -> 1.570796
ASIN(X)
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);
        -> 0.201358
mysql> SELECT ASIN('foo');
        -> 0.000000
ATAN(X)
Returns the arc tangent of X, that is, the value whose tangent is X:
mysql> SELECT ATAN(2);
        -> 1.107149
mysql> SELECT ATAN(-2);
        -> -1.107149
ATAN(Y,X)
ATAN2(Y,X)
Returns the arc tangent of the two variables X and Y. It is similar to calculating the arc tangent of Y / X, except that the signs of both arguments are used to determine the quadrant of the result:
mysql> SELECT ATAN(-2,2);
        -> -0.785398
mysql> SELECT ATAN2(PI(),0);
        -> 1.570796
CEILING(X)
CEIL(X)
Returns the smallest integer value not less than X:
mysql> SELECT CEILING(1.23);
        -> 2
mysql> SELECT CEIL(-1.23);
        -> -1
The CEIL() alias was added in version 4.0.6. Note that the return value is converted to a BIGINT!
COS(X)
Returns the cosine of X, where X is given in radians:
mysql> SELECT COS(PI());
        -> -1.000000
COT(X)
Returns the cotangent of X:
mysql> SELECT COT(12);
        -> -1.57267341
mysql> SELECT COT(0);
        -> NULL
CRC32(expr)
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 be a string and will be treated as one if it is not.
mysql> SELECT CRC32('MySQL');
        -> 3259397556
CRC32() is available as of MySQL 4.1.0.
DEGREES(X)
Returns the argument X, converted from radians to degrees:
mysql> SELECT DEGREES(PI());
        -> 180.000000
DIV
Integer division. Similar to FLOOR() but safe with BIGINT values.
mysql> SELECT 5 DIV 2
        -> 2
DIV is new in MySQL 4.1.0.
EXP(X)
Returns the value of e (the base of natural logarithms) raised to the power of X:
mysql> SELECT EXP(2);
        -> 7.389056
mysql> SELECT EXP(-2);
        -> 0.135335
FLOOR(X)
Returns the largest integer value not greater than X:
mysql> SELECT FLOOR(1.23);
        -> 1
mysql> SELECT FLOOR(-1.23);
        -> -2
Note that the return value is converted to a BIGINT!
GREATEST(X,Y,...)
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"
In MySQL versions prior to Version 3.22.5, you can use MAX() instead of GREATEST.
LEAST(X,Y,...)
With two or more arguments, returns the smallest (minimum-valued) argument. The arguments are compared using the following rules:
mysql> SELECT LEAST(2,0);
        -> 0
mysql> SELECT LEAST(34.0,3.0,5.0,767.0);
        -> 3.0
mysql> SELECT LEAST("B","A","C");
        -> "A"
In MySQL versions prior to Version 3.22.5, you can use MIN() instead of LEAST. Note that the above conversion rules can produce strange results in some borderline cases:
SELECT CAST(least(3600, 9223372036854775808.0) as SIGNED);
 -> -9223372036854775808
This happens because MySQL reads 9223372036854775808.0 in an integer context and the integer representation is not good enough to hold the value so it's wraps to a signed integer.
LN(X)
Returns the natural logarithm of X:
mysql> SELECT LN(2);
        -> 0.693147
mysql> SELECT LN(-2);
        -> NULL
This function was added in MySQL version 4.0.3. It is synonymous with LOG(X) in MySQL.
LOG(X)
LOG(B,X)
If called with one parameter, this function returns the natural logarithm of X:
mysql> SELECT LOG(2);
        -> 0.693147
mysql> SELECT LOG(-2);
        -> NULL
If called with two parameters, this function returns the logarithm of X for an arbitary base B:
mysql> SELECT LOG(2,65536);
        -> 16.000000
mysql> SELECT LOG(1,100);
        -> NULL
The arbitrary base option was added in MySQL version 4.0.3. LOG(B,X) is equivalent to LOG(X)/LOG(B).
LOG2(X)
Returns the base-2 logarithm of X:
mysql> SELECT LOG2(65536);
        -> 16.000000
mysql> SELECT LOG2(-100);
        -> NULL
LOG2() is useful for finding out how many bits a number would require for storage. This function was added in MySQL version 4.0.3. In earlier versions, you can use LOG(X)/LOG(2) instead.
LOG10(X)
Returns the base-10 logarithm of X:
mysql> SELECT LOG10(2);
        -> 0.301030
mysql> SELECT LOG10(100);
        -> 2.000000
mysql> SELECT LOG10(-100);
        -> NULL
MOD(N,M)
%
Modulo (like the % operator in C). 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. The last example works only in MySQL 4.1
PI()
Returns the value of PI. The default shown number of decimals is 5, but MySQL internally uses the full double precession for PI.
mysql> SELECT PI();
        -> 3.141593
mysql> SELECT PI()+0.000000000000000000;
        -> 3.141592653589793116
POW(X,Y)
POWER(X,Y)
Returns the value of X raised to the power of Y:
mysql> SELECT POW(2,2);
        -> 4.000000
mysql> SELECT POW(2,-2);
        -> 0.250000
RADIANS(X)
Returns the argument X, converted from degrees to radians:
mysql> SELECT RADIANS(90);
        -> 1.570796
RAND()
RAND(N)
Returns a random floating-point value in the range 0 to 1.0. If an integer argument N is specified, it is used as the seed value (producing a repeatable sequence):
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
You can't use a column with RAND() values in an ORDER BY clause, because ORDER BY would evaluate the column multiple times. From version 3.23 you can do: SELECT * FROM table_name ORDER BY RAND() This is useful to get a random sample of a set SELECT * FROM table1,table2 WHERE a=b AND c<d ORDER BY RAND() LIMIT 1000. Note that a RAND() in a WHERE clause will be re-evaluated every time the WHERE is executed. RAND() is not meant to be a perfect random generator, but instead a fast way to generate ad hoc random numbers that will be portable between platforms for the same MySQL version.
ROUND(X)
ROUND(X,D)
Returns the argument X, rounded to the nearest integer. With two arguments, rounded to a number to D decimals.
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
Note that the behavior of ROUND() when the argument is halfway between two integers depends on the C library implementation. Some 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.
SIGN(X)
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
SIN(X)
Returns the sine of X, where X is given in radians:
mysql> SELECT SIN(PI());
        -> 0.000000
SQRT(X)
Returns the non-negative square root of X:
mysql> SELECT SQRT(4);
        -> 2.000000
mysql> SELECT SQRT(20);
        -> 4.472136
TAN(X)
Returns the tangent of X, where X is given in radians:
mysql> SELECT TAN(PI()+1);
        -> 1.557408
TRUNCATE(X,D)
Returns the number X, truncated to D decimals. If D is 0, the result will have no decimal point or fractional part:
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
Starting from MySQL 3.23.51, all numbers are rounded toward zero. If D is negative, the whole part of the number is zeroed out:
mysql> SELECT TRUNCATE(122,-2);
       -> 100
Note that decimal numbers are normally not stored as exact numbers in computers, but as double-precision values, so you may be fooled by the following result:
mysql> SELECT TRUNCATE(10.28*100,0);
       -> 1027
The above happens because 10.28 is actually stored as something like 10.2799999999999999.

12.4 Date and Time Functions

This section describes the functions that can be used to manipulate temporal values. See section 11.2 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.

Here is an example that uses date functions. The following query selects all records with a date_col value from within the last 30 days:

mysql> SELECT something FROM tbl_name
           WHERE TO_DAYS(NOW()) - TO_DAYS(date_col) <= 30;

(Note that the query will also select records with dates that lie in the future.)

Functions that expect date values usually will accept datetime values and ignore the time part. Functions that expect time values usually will 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 will always produce the same result. This principle also applies to CURDATE(), CURTIME(), UTC_DATE(), UTC_TIME(), UTC_TIMESTAMP(), and any of their synonyms.

The return value ranges in the following function descriptions apply for complete dates. If a date is a ``zero'' value or an incomplete date such as '2001-11-00', functions that extract a part of a date may return 0. For example, DAYOFMONTH('2001-11-00') returns 0.

ADDDATE(date,INTERVAL expr type)
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().
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'
As of MySQL 4.1.1, the second syntax is allowed, where expr is a date or datetime expression and days is the number of days to be added to expr.
mysql> SELECT ADDDATE('1998-01-02', 31);
        -> '1998-02-02'
ADDTIME(expr,expr2)
ADDTIME() adds expr2 to expr and returns the result. expr is a date 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'
ADDTIME() was added in MySQL 4.1.1.
CURDATE()
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
CURRENT_DATE()
CURRENT_DATE and CURRENT_DATE() are synonyms for CURDATE().
CURTIME()
Returns the current time as a value in 'HH:MM:SS' or HHMMSS format, depending on whether the function is used in a string or numeric context:
mysql> SELECT CURTIME();
        -> '23:50:26'
mysql> SELECT CURTIME() + 0;
        -> 235026
CURRENT_TIME
CURRENT_TIME()
CURRENT_TIME and CURRENT_TIME() are synonyms for CURTIME().
CURRENT_TIMESTAMP
CURRENT_TIMESTAMP()
CURRENT_TIMESTAMP and CURRENT_TIMESTAMP() are synonyms for NOW().
DATE(expr)
Extracts the date part of the date or datetime expression expr.
mysql> SELECT DATE('2003-12-31 01:02:03');
        -> '2003-12-31'
DATE() is available as of MySQL 4.1.1.
DATEDIFF(expr,expr2)
DATEDIFF() returns the number of days between the start date expr and the end date expr2. expr 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('1997-11-31 23:59:59','1997-12-31');
        -> -30
DATEDIFF() was added in MySQL 4.1.1.
DATE_ADD(date,INTERVAL expr type)
DATE_SUB(date,INTERVAL expr type)
These functions perform date arithmetic. As of MySQL Version 3.23, INTERVAL expr type is allowed on either side of the + operator if the expression on the other side is a date or datetime value. For the - operator, INTERVAL expr type is allowed only on the right side, because it makes no sense to subtract a date or datetime value from an interval. (See examples below.) date is a DATETIME or DATE value specifying the starting date. 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. type is a keyword indicating how the expression should be interpreted. The following table shows how the type and expr arguments are related:
type 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 type values DAY_MICROSECOND, HOUR_MICROSECOND, MINUTE_MICROSECOND, SECOND_MICROSECOND, and MICROSECOND are allowed as of MySQL 4.1.1. The values QUARTER and WEEK are allowed as of MySQL 5.0.0. 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:
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 type keyword), MySQL assumes you have left out the leftmost parts of the interval value. For example, if you specify a type 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 time of day. Note that 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 use really malformed dates, the result is NULL. 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'
Note from the preceding example that the keyword INTERVAL and the type specifier are not case sensitive.
DATE_FORMAT(date,format)
Formats the date value according to the format string. The following specifiers may be used in the format string:
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, etc.)
%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, 4 digits; used with %V
%x Year for the week, where Monday is the first day of the week, numeric, 4 digits; used with %v
%Y Year, numeric, 4 digits
%y Year, numeric, 2 digits
%% A literal `%'.
All other characters are just copied to the result without interpretation. The %f format specifier is available as of MySQL 4.1.1. As of MySQL Version 3.23, the `%' character is required before format specifier characters. In earlier versions of MySQL, `%' was optional. The reason the ranges for the month and day specifiers begin with zero is that MySQL allows incomplete dates such as '2004-00-00' to be stored as of MySQL 3.23.
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'
DAY(date)
DAY() is a synonym for DAYOFMONTH(). It is available as of MySQL 4.1.1.
DAYNAME(date)
Returns the name of the weekday for date:
mysql> SELECT DAYNAME('1998-02-05');
        -> 'Thursday'
DAYOFMONTH(date)
Returns the day of the month for date, in the range 1 to 31:
mysql> SELECT DAYOFMONTH('1998-02-03');
        -> 3
DAYOFWEEK(date)
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
DAYOFYEAR(date)
Returns the day of the year for date, in the range 1 to 366:
mysql> SELECT DAYOFYEAR('1998-02-03');
        -> 34
EXTRACT(type FROM date)
The EXTRACT() function uses the same kinds of interval type 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 10:30:00.00123");
        -> 123
FROM_DAYS(N)
Given a daynumber N, returns a DATE value:
mysql> SELECT FROM_DAYS(729669);
        -> '1997-10-07'
FROM_DAYS() is not intended for use with values that precede the advent of the Gregorian calendar (1582), because it doesn't take into account the days that were lost when the calendar was changed.
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 format, depending on whether the function is used in a string or numeric context:
mysql> SELECT FROM_UNIXTIME(875996580);
        -> '1997-10-04 22:23:00'
mysql> SELECT FROM_UNIXTIME(875996580) + 0;
        -> 19971004222300
If format is given, the result is formatted according to the format string. format may contain the same specifiers as those listed in the entry for the DATE_FORMAT() function:
mysql> SELECT FROM_UNIXTIME(UNIX_TIMESTAMP(),
    ->                      '%Y %D %M %h:%i:%s %x');
        -> '2003 6th August 06:22:58 2003'
GET_FORMAT(DATE | TIME | TIMESTAMP, '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 three possible values for the first argument and the five possible values for the second argument result in 15 possible format strings (for the specifiers used, see the table in the DATE_FORMAT() function description):
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(TIMESTAMP,'USA') '%Y-%m-%d-%H.%i.%s'
GET_FORMAT(TIMESTAMP,'JIS') '%Y-%m-%d %H:%i:%s'
GET_FORMAT(TIMESTAMP,'ISO') '%Y-%m-%d %H:%i:%s'
GET_FORMAT(TIMESTAMP,'EUR') '%Y-%m-%d-%H.%i.%s'
GET_FORMAT(TIMESTAMP,'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'
ISO format is ISO 9075, not ISO 8601.
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
GET_FORMAT() is available as of MySQL 4.1.1. See See section 13.5.3.1 SET Syntax.
HOUR(time)
Returns the hour for time. The range of the return value will be 0 to 23 for time-of-day values:
mysql> SELECT HOUR('10:05:03');
        -> 10
However, the range of TIME values actually is much larger, so HOUR can return values greater than 23:

mysql> SELECT HOUR('272:59:59');
        -> 272
LAST_DAY(date)
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'), LAST_DAY('2004-02-05');
        -> '2003-02-28', '2004-02-29'
mysql> SELECT LAST_DAY('2004-01-01 01:01:01');
        -> '2004-01-31'
mysql> SELECT LAST_DAY('2003-03-32');
        -> NULL
LAST_DAY() is available as of MySQL 4.1.1.
LOCALTIME
LOCALTIME()
LOCALTIME and LOCALTIME() are synonyms for NOW().
LOCALTIMESTAMP
LOCALTIMESTAMP()
LOCALTIMESTAMP and LOCALTIMESTAMP() are synonyms for NOW().
MAKEDATE(year,dayofyear)
Returns a date, given year and day-of-year values. dayofyear must be greater than 0 or the result will 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
MAKEDATE() is available as of MySQL 4.1.1.
MAKETIME(hour,minute,second)
Returns a time value calculated from the hour, minute, and second arguments.
mysql> SELECT MAKETIME(12,15,30);
        -> '12:15:30'
MAKETIME() is available as of MySQL 4.1.1.
MICROSECOND(expr)
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
MICROSECOND() is available as of MySQL 4.1.1.
MINUTE(time)
Returns the minute for time, in the range 0 to 59:
mysql> SELECT MINUTE('98-02-03 10:05:03');
        -> 5
MONTH(date)
Returns the month for date, in the range 1 to 12:
mysql> SELECT MONTH('1998-02-03');
        -> 2
MONTHNAME(date)
Returns the name of the month for date:
mysql> SELECT MONTHNAME('1998-02-05');
        -> 'February'
NOW()
Returns the current date and time as a value in 'YYYY-MM-DD HH:MM:SS' or YYYYMMDDHHMMSS format, depending on whether the function is used in a string or numeric context:
mysql> SELECT NOW();
        -> '1997-12-15 23:50:26'
mysql> SELECT NOW() + 0;
        -> 19971215235026
PERIOD_ADD(P,N)
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
PERIOD_DIFF(P1,P2)
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
QUARTER(date)
Returns the quarter of the year for date, in the range 1 to 4:
mysql> SELECT QUARTER('98-04-01');
        -> 2
SECOND(time)
Returns the second for time, in the range 0 to 59:
mysql> SELECT SECOND('10:05:03');
        -> 3
SEC_TO_TIME(seconds)
Returns the seconds argument, converted to hours, minutes, and seconds, as a value in 'HH:MM:SS' or HHMMSS format, depending on whether the function is used in a string or numeric context:
mysql> SELECT SEC_TO_TIME(2378);
        -> '00:39:38'
mysql> SELECT SEC_TO_TIME(2378) + 0;
        -> 3938
STR_TO_DATE(str,format)
This is the reverse function of the DATE_FORMAT() function. It takes a string str, and a format string format, and returns a DATETIME value. 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 table in the DATE_FORMAT() function description. All other characters are just taken verbatim, thus not being interpreted. If str contains an illegal date, time, or datetime value, STR_TO_DATE() returns NULL.
mysql> SELECT STR_TO_DATE('03.10.2003 09.20', '%d.%m.%Y %H.%i');
        -> '2003-10-03 09:20:00'
mysql> SELECT STR_TO_DATE('10arp', '%carp');
        -> '0000-10-00 00:00:00'
mysql> SELECT STR_TO_DATE('2003-15-10 00:00:00', '%Y-%m-%d %H:%i:%s');
        -> NULL
STR_TO_DATE() is available as of MySQL 4.1.1.
SUBDATE(date,INTERVAL expr type)
SUBDATE(expr,days)
When invoked with the INTERVAL form of the second argument, SUBDATE() is a synonym for DATE_SUB().
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'
As of MySQL 4.1.1, the second syntax is allowed, where expr is a date or datetime expression and days is the number of days to be subtracted from expr.
mysql> SELECT SUBDATE('1998-01-02 12:00:00', 31);
        -> '1997-12-02 12:00:00'
SUBTIME(expr,expr2)
SUBTIME() subtracts expr2 from expr and returns the result. expr is a date 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'
SUBTIME() was added in MySQL 4.1.1.
SYSDATE()
SYSDATE() is a synonym for NOW().
TIME(expr)
Extracts the time part of the time or datetime expression expr.
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'
TIME() is available as of MySQL 4.1.1.
TIMEDIFF(expr,expr2)
TIMEDIFF() returns the time between the start time expr and the end time expr2. expr 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'
TIMEDIFF() was added in MySQL 4.1.1.
TIMESTAMP(expr)
TIMESTAMP(expr,expr2)
With one argument, returns the date or datetime expression expr as a datetime value. With two arguments, adds the time expression expr2 to the date or datetime expression expr and returns 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'
TIMESTAMP() is available as of MySQL 4.1.1.
TIMESTAMPADD(interval,int_expr,datetime_expr)
Adds the integer expression int_expr to the date or datetime expression datetime_expr. The unit for int_expr is given by the interval argument, which should be one of the following values: FRAC_SECOND, SECOND, MINUTE, HOUR, DAY, WEEK, MONTH, QUARTER, or YEAR. The interval value may be specified using one of keywords as shown, or with a prefix of SQL_TSI_. For example, DAY or 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(interval,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 interval argument. The legal values for interval are the same as those described in the desription 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.
TIME_FORMAT(time,format)
This is used like the DATE_FORMAT() function, but the format string may contain only those format specifiers that handle 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'
TIME_TO_SEC(time)
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
TO_DAYS(date)
Given a date date, returns a daynumber (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 doesn't take into account the days that were lost when the calendar was changed.
UNIX_TIMESTAMP()
UNIX_TIMESTAMP(date)
If called with no argument, returns a Unix timestamp (seconds since '1970-01-01 00:00:00' GMT) 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' GMT. date may be a DATE string, a DATETIME string, a TIMESTAMP, or a number in the format YYMMDD or YYYYMMDD in local time:
mysql> SELECT UNIX_TIMESTAMP();
        -> 882226357
mysql> SELECT UNIX_TIMESTAMP('1997-10-04 22:23:00');
        -> 875996580
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, but please note that only basic checking is performed (year 1970-2037, month 01-12, day 01-31). If you want to subtract UNIX_TIMESTAMP() columns, you might want to cast the result to signed integers. See section 12.5 Cast Functions.
UTC_DATE
UTC_DATE()
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
UTC_DATE() is available as of MySQL 4.1.1.
UTC_TIME
UTC_TIME()
Returns the current UTC time as a value in 'HH:MM:SS' or HHMMSS 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
UTC_TIME() is available as of MySQL 4.1.1.
UTC_TIMESTAMP
UTC_TIMESTAMP()
Returns the current UTC date and time as a value in 'YYYY-MM-DD HH:MM:SS' or YYYYMMDDHHMMSS 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
UTC_TIMESTAMP() is available as of MySQL 4.1.1.
WEEK(date [,mode])
The 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 0-53 or 1-52. When mode argument is omitted the value of a default_week_format server variable (or 0 in MySQL 4.0 or earlier) is assumed. See section 13.5.3.1 SET Syntax. The following table demonstrates how the mode argument works:
Value Meaning
0 Week starts on Sunday; return value range is 0 to 53; week 1 is the first week that starts in this year
1 Week starts on Monday; return value range is 0 to 53; week 1 is the first week that has more than 3 days in this year
2 Week starts on Sunday; return value range is 1 to 53; week 1 is the first week that starts in this year
3 Week starts on Monday; return value range is 1 to 53; week 1 is the first week that has more than 3 days in this year
4 Week starts on Sunday; return value range is 0 to 53; week 1 is the first week that has more than 3 days in this year
5 Week starts on Monday; return value range is 0 to 53; week 1 is the first week that starts in this year
6 Week starts on Sunday; return value range is 1 to 53; week 1 is the first week that has more than 3 days in this year
7 Week starts on Monday; return value range is 1 to 53; week 1 is the first week that starts in this year
The mode value of 3 can be used as of MySQL 4.0.5. The mode value of 4 and above can be used as of MySQL 4.0.17.
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: In Version 4.0, WEEK(date,0) was changed to match the calendar in the USA. Before that, WEEK() was calculated incorrectly for dates in USA. (In effect, WEEK(date) and WEEK(date,0) was incorrect for all cases.) Note that if a date falls in the last week of the previous year, MySQL will return 0 if you don't 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 as we want the function to return ``the week number in the given year.'' This makes the usage 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, you should use 2, 3, 6, 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'
WEEKDAY(date)
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
WEEKOFYEAR(date)
Returns the calendar week of the date as a number in the range from 1 to 53.
mysql> SELECT WEEKOFYEAR('1998-02-20');
        -> 8
WEEKOFYEAR() is available as of MySQL 4.1.1.
YEAR(date)
Returns the year for date, in the range 1000 to 9999:
mysql> SELECT YEAR('98-02-03');
        -> 1998
YEARWEEK(date)
YEARWEEK(date,start)
Returns year and week for a date. The start argument works exactly like the start argument to WEEK(). Note that 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.

12.5 Cast Functions

The CAST() and CONVERT() functions may be used to take a value of one type and produce a value of another type. Their syntax is:

CAST(expression AS type)
CONVERT(expression,type)
CONVERT(expr USING transcoding_name)

The type value can be one of the following:

CAST() and CONVERT() are available as of MySQL 4.0.2. The CHAR conversion type is available as of 4.0.6. The USING form of CONVERT() is available as of 4.1.0.

CAST() and CONVERT(... USING ...) are SQL-99 syntax. The non-USING form of CONVERT() is ODBC syntax.

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:

SELECT enum_col FROM tbl_name ORDER BY CAST(enum_col AS CHAR);

CAST(string AS BINARY) is the same thing as BINARY string. CAST(expr AS CHAR) treats the expression as a string with the default character set.

NOTE: In MysQL 4.0 the CAST() to DATE, DATETIME, or TIME only marks the column to be a specific type but doesn't change the value of the column.

In MySQL 4.1.0 the value is converted to the correct column type when it's sent to the user (this is a feature of how the new protocol in 4.1 sends date information to the client):

mysql> SELECT CAST(NOW() AS DATE);
       -> 2003-05-26

In later MySQL versions (probably 4.1.2 or 5.0) we will fix that CAST also changes the result if you use it as part of a more complex expression, like 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 12.4 Date and Time Functions.

To cast a string to a numeric value, you don't normally have to do anything; just use the string value as it would be a number:

mysql> SELECT 1+'1';
       -> 2

If you use a number in string context, the number automatically will be 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 numerical operations (like +) and one of the operands is unsigned integer, the result will be 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 above rule. (In this context, DECIMAL 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.

The handing of unsigned values was changed in MySQL 4.0 to be able to support BIGINT values properly. If you have some code that you want to run in both MySQL 4.0 and 3.23 (in which case you probably can't use the CAST() function), you can use the following technique to get a signed result when subtracting two unsigned integer columns:

SELECT (unsigned_column_1+0.0)-(unsigned_column_2+0.0);

The idea is that the columns are converted to floating-point values before the subtraction occurs.

If you get a problem with UNSIGNED columns in your old MySQL application when porting to MySQL 4.0, you can use the --sql-mode=NO_UNSIGNED_SUBTRACTION option when starting mysqld. Note however that as long as you use this, you will not be able to make efficient use of the BIGINT UNSIGNED column type.

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 server's default character set to the corresponding string in the utf8 character set:

SELECT CONVERT('abc' USING utf8);

12.6 Other Functions

12.6.1 Bit Functions

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. XOR was added in version 4.0.2.
<<
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.
BIT_COUNT(N)
Returns the number of bits that are set in the argument N:
mysql> SELECT BIT_COUNT(29);
        -> 4

12.6.2 Encryption Functions

AES_ENCRYPT(string,key_string)
AES_DECRYPT(string,key_string)
These functions allow encryption/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 usually secure enough. 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 as 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'));
You can get even more security by not transferring the key over the connection for each query, which can be accomplished by storing it in a server-side variable at connection time. For example:
SELECT @password:='my password';
INSERT INTO t VALUES (1,AES_ENCRYPT('text',@password));
AES_ENCRYPT() and AES_DECRYPT() were added in version 4.0.2, and can be considered the most cryptographically secure encryption functions currently available in MySQL.
DECODE(crypt_str,pass_str)
Descrypts the encrypted string crypt_str using pass_str as the password. crypt_str should be a string returned from ENCODE().
ENCODE(str,pass_str)
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 string. If you want to save it in a column, use a BLOB column type.
DES_DECRYPT(string_to_decrypt [, key_string])
Decrypts a string encrypted with DES_ENCRYPT(). Note that this function works only if MySQL has been configured with SSL support. See section 5.5.8 Using Secure Connections. If no key_string 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. If you pass this function a key_string argument, that string is used as the key for decrypting the message. If the string_to_decrypt doesn't look like an encrypted string, MySQL will return the given string_to_decrypt. On error, this function returns NULL.
DES_ENCRYPT(string_to_encrypt [, (key_number | key_string) ] )
Encrypts the string with the given key using the Triple-DES algorithm. Note that this function works only if MySQL has been configured with SSL support. See section 5.5.8 Using Secure Connections. The encryption key to use is chosen the following way:
Argument Description
Only one argument The first key from des-key-file is used.
key number The given key (0-9) from the des-key-file is used.
string The given key_string will be used to crypt string_to_encrypt.
The return string will be a binary string where the first character will be CHAR(128 | key_number). The 128 is added to make it easier to recognize an encrypted key. If you use a string key, key_number will be 127. On error, this function returns NULL. The string length for the result will be new_length= orig_length + (8-(orig_length % 8))+1. The des-key-file has the following format:
key_number des_key_string
key_number des_key_string
Each key_number must be a number in the range from 0 to 9. Lines in the file may be in any order. des_key_string is the string that will be used to encrypt the message. Between the number and the key there should be at least one space. The first key is the default key that will be used if you don't 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 command. This requires the Reload_priv 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");
ENCRYPT(str[,salt])
Encrypt str using the Unix crypt() system call. The salt argument should be a string with two characters. (As of MySQL Version 3.22.16, salt may be longer than two characters.)
mysql> SELECT ENCRYPT("hello");
        -> 'VxuFAJXVARROc'
ENCRYPT() ignores all but the first 8 characters of str, at least on some systems. This behavior is determined by the implementation of the underlying crypt() system call. If crypt() is not available on your system, ENCRYPT() always returns NULL. Because of this we recommend that you use MD5() or SHA1() instead; these two functions exist on all platforms.
MD5(string)
Calculates an MD5 128-bit checksum for the string. The value is returned as a 32-digit hex number that may, for example, be used as a hash key:
mysql> SELECT MD5("testing");
        -> 'ae2b1fca515949e5d54fb22b8ed95575'
This is the "RSA Data Security, Inc. MD5 Message-Digest Algorithm".
PASSWORD(str)
OLD_PASSWORD(str)
Calculates a password string from the plaintext password str. 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');
        -> '7f84554057dd964b'
PASSWORD() encryption is irreversible. PASSWORD() does not perform password encryption in the same way that Unix passwords are encrypted. See ENCRYPT(). Note: The PASSWORD() function is used by the authentication system in MySQL Server, you should NOT use it in your own applications. For that purpose, use MD5() or SHA1() instead. Also see RFC-2195 for more information about handling passwords and authentication securely in your application.
SHA1(string)
SHA(string)
Calculates an SHA1 160-bit checksum for the string, as described in RFC 3174 (Secure Hash Algorithm). The value is returned as a 40-digit hex number, or NULL in case the input argument was NULL. One of the possible uses for this function is as a hash key. You can also use it as cryptographically safe function for storing passwords.
mysql> SELECT SHA1("abc");
        -> 'a9993e364706816aba3e25717850c26c9cd0d89d'
SHA1() was added in version 4.0.2, and can be considered a cryptographically more secure equivalent of MD5(). SHA() is synonym for SHA1().

12.6.3 Information Functions

BENCHMARK(count,expr)
The BENCHMARK() function executes the expression expr repeatedly count times. It may be used to time how fast MySQL processes the expression. The result value is always 0. The intended use is in 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 may be advisable to execute BENCHMARK() several times, and interpret the result with regard to how heavily loaded the server machine is.
CHARSET(str)
Returns the character set of the string argument.
mysql> SELECT CHARSET(_utf8'abc');
        -> 'utf8'
CHARSET() was added in version 4.1.0.
COERCIBILITY(str)
Returns the collation coercibility value of the string argument.
mysql> SELECT COERCIBILITY('abc' COLLATE latin1_swedish_ci);
        -> 0
mysql> SELECT COERCIBILITY('abc');
        -> 3
mysql> SELECT COERCIBILITY(USER());
        -> 2
The return values have the following meanings:
0 Explicit collation
1 No collation
2 Implicit collation
3 Coercible
Lower values have higher precedence. COERCIBILITY() was added in version 4.1.1.
COLLATION(str)
Returns the collation for the character set of the string argument.
mysql> SELECT COLLATION('abc');
        -> 'latin1_swedish_ci'
mysql> SELECT COLLATION(_utf8'abc');
        -> 'utf8_general_ci'
COLLATION() was added in version 4.1.0.
CONNECTION_ID()
Returns the connection ID (thread ID) for the connection. Every connection has its own unique ID:
mysql> SELECT CONNECTION_ID();
        -> 23786
CURRENT_USER()
Returns the username and hostname that the current session was authenticated as. This value corresponds to the account that is used for assessing your access privileges. It may be different than 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.
DATABASE()
Returns the current database name:
mysql> SELECT DATABASE();
        -> 'test'
If there is no current database, DATABASE() returns NULL as of MySQL 4.1.1, and the empty string before that.
FOUND_ROWS()
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 get this row count, include a SQL_CALC_FOUND_ROWS option in the SELECT statement, 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 will return a number indicating how many rows the first SELECT would have returned had it been written without the LIMIT clause. (If the preceding SELECT statement does not include the SQL_CALC_FOUND_ROWS option, then FOUND_ROWS() may return a different result when LIMIT is used than when it is not.) Note that if you are using SELECT SQL_CALC_FOUND_ROWS ... MySQL has to 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 queries 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: SQL_CALC_FOUND_ROWS and FOUND_ROWS() are available starting at MySQL version 4.0.0.
LAST_INSERT_ID([expr])
Returns the last automatically generated value that was inserted into an AUTO_INCREMENT column.
mysql> SELECT LAST_INSERT_ID();
        -> 195
The last ID that was generated is maintained in the server on a per-connection basis. This means the value the function returns to a given client is the most recent AUTO_INCREMENT value generated by that client. The value cannot be affected by other clients, even if they generate AUTO_INCREMENT values of their own. This behavior ensures that you can retrieve your 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 update the AUTO_INCREMENT column of a row with a non-magic value (that is, a value that is not NULL and not 0). If you insert many rows at the same time with an insert statement, LAST_INSERT_ID() returns the value for the first inserted row. The reason for this is to make it possible to easily reproduce the same INSERT statement against some other server. If expr is given as an argument to LAST_INSERT_ID(), then the value of the argument is returned by the function, and is set as the next value to be returned by LAST_INSERT_ID(). This can be used to simulate sequences: 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 can't use the C API function to retrieve the value for LAST_INSERT_ID(expr) after executing other SQL statements like SELECT or SET.
SESSION_USER()
SESSION_USER() is a synonym for USER().
SYSTEM_USER()
SYSTEM_USER() is a synonym for USER().
USER()
Returns the current MySQL username and hostname:
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. (Prior to MySQL Version 3.22.11, the function value does not include the client hostname.) You can extract just the username part, regardless of whether the value includes a hostname part, like this:
mysql> SELECT SUBSTRING_INDEX(USER(),'@',1);
        -> 'davida'
VERSION()
Returns a string indicating the MySQL server version:
mysql> SELECT VERSION();
        -> '3.23.13-log'
Note that if your version ends with -log this means that logging is enabled.

12.6.4 Miscellaneous Functions

FORMAT(X,D)
Formats the number X to a format like '#,###,###.##', rounded to D decimals, and returns the result as a string. If D is 0, the result will have 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'
GET_LOCK(str,timeout)
Tries to obtain a lock with a name given by the string str, with 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 already locked the name), or NULL if an error occurred (such as running out of memory or the thread was killed with mysqladmin kill). A lock is released when you execute RELEASE_LOCK(), execute a new GET_LOCK(), or the thread terminates (either normally or abnormally). 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:
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
Note that the second RELEASE_LOCK() call returns NULL because the lock 'lock1' was automatically released by the second GET_LOCK() call.
INET_ATON(expr)
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 example the above number is calculated as 209*256^3 + 207*256^2 + 224*256 +40. As of MySQL 4.1.2, INET_ATON() also understands short-form IP addresses:
mysql> SELECT INET_ATON('127.0.0.1'), INET_ATON('127.1');
        -> 2130706433, 2130706433
INET_NTOA(expr)
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"
IS_FREE_LOCK(str)
Checks if 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 on errors (such as incorrect arguments). IS_FREE_LOCK() was added in MySQL version 4.0.2.
IS_USED_LOCK(str)
Checks if 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. IS_USED_LOCK() was added in MySQL version 4.1.0.
MASTER_POS_WAIT(log_name, log_pos [, timeout])
Blocks until the slave reaches (that is, has read and applied all updates up to) the specified position in the master log. If master information is not initialized, or if the arguments are incorrect, returns NULL. If the slave is not running, will block and wait until it is started and goes to or past the specified position. If the slave is already past the specified position, returns immediately. If timeout (new in 4.0.10) is specified, will give up waiting when timeout seconds have elapsed. timeout must be greater than 0; a zero or negative timeout means no timeout. The return value is the number of log events it had to wait to get to the specified position, or NULL in case of error, or -1 if the timeout has been exceeded. This command is useful for control of master/slave synchronization.
RELEASE_LOCK(str)
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 wasn't locked by this thread (in which case the lock is not released), and NULL if the named lock didn't exist. (The lock will not exist if it was never obtained by a call to GET_LOCK() or if it already has been released.) The DO statement is convenient to use with RELEASE_LOCK(). See section 13.1.2 DO Syntax.
UUID()
Returns a UUID--a Universal Unique Identifier--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). A UUID is designed as a number that is unique globally in space and time. Two calls to UUID() are expected to generate two different values, even if these calls were performed on two separate computers that are not connected to each other. A UUID is a 128-bit number represented by a string of 5 hexadecimal numbers in aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee format:
mysql> SELECT UUID();
        -> '6ccd780c-baba-1026-9564-0040f4311e29'

12.7 Functions and Modifiers for Use with GROUP BY Clauses

12.7.1 GROUP BY Functions

If you use a group function in a statement containing no GROUP BY clause, it is equivalent to grouping on all rows.

AVG(expr)
Returns the average value of expr:
mysql> SELECT student_name, AVG(test_score)
    ->        FROM student
    ->        GROUP BY student_name;
BIT_AND(expr)
Returns the bitwise AND of all bits in expr. The calculation is performed with 64-bit (BIGINT) precision. As of MySQL 4.0.17, this function returns 18446744073709551615 if there were no matching rows. (This is an unsigned BIGINT value with all bits set to 1.) Before 4.0.17, the function returns -1 if there were no matching rows.
BIT_OR(expr)
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.
BIT_XOR(expr)
Returns the bitwise XOR of all bits in expr. The calculation is performed with 64-bit (BIGINT) precision. Function returns 0 if there were no matching rows. This function is available as of MySQL 4.1.1.
COUNT(expr)
Returns a count of the number of non-NULL values in the rows retrieved by a SELECT statement:
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 and ISAM tables only, because an exact record count is stored for these table types and can be accessed very quickly. For transactional storage engines (InnodB, 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:
mysql> SELECT COUNT(DISTINCT results) FROM student;
In MySQL you can get the number of distinct expression combinations that don't contain NULL by giving a list of expressions. In SQL-99 you would have to do a concatenation of all expressions inside COUNT(DISTINCT ...).
GROUP_CONCAT(expr)
Full syntax:
GROUP_CONCAT([DISTINCT] expr [,expr ...]
             [ORDER BY {unsigned_integer | col_name | formula}
                 [ASC | DESC] [,col ...]]
             [SEPARATOR str_val])
This function was added in MySQL version 4.1. It returns a string result with the concatenated values from a group:
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 the string value which should be inserted between values of result. The default is a comma (`","'). You can remove the separator altogether by specifying SEPARATOR "". You can set a maximum allowed length with the variable group_concat_max_len in your configuration. The syntax to do this at runtime is:
SET [SESSION | GLOBAL] group_concat_max_len = unsigned_integer;
If a maximum length has been set, the result is truncated to this maximum length. The GROUP_CONCAT() function is an enhanced implementation of the basic LIST() function supported by Sybase SQL Anywhere. GROUP_CONCAT() is backward compatible with the extremely limited functionality of LIST(), if only one column and no other options are specified. LIST() does have a default sorting order.
MIN(expr)
MAX(expr)
Returns the minimum or maximum value of expr. MIN() and MAX() may take a string argument; in such cases they return the minimum or maximum string value. See section 7.4.5 How MySQL Uses Indexes.
mysql> SELECT student_name, MIN(test_score), MAX(test_score)
    ->        FROM student
    ->        GROUP BY student_name;
In MIN(), MAX() and other aggregate functions, MySQL currently compares ENUM and SET columns by their string value rather than by the string's relative position in the set. This will be rectified.
STD(expr)
STDDEV(expr)
Returns the standard deviation of expr (the square root of VARIANCE(). This is an extension to SQL-99. The STDDEV() form of this function is provided for Oracle compatibility.
SUM(expr)
Returns the sum of expr. Note that if the return set has no rows, it returns NULL!
VARIANCE(expr)
Returns the standard variance of expr (considering rows as the whole population, not as a sample; so it has the number of rows as denominator). This is an extension to SQL-99 (available only in version 4.1 or later).

12.7.2 GROUP BY Modifiers

As of MySQL 4.1.1, 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.

As an illustration, 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:

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 |
+------+---------+------------+-------------+

Note that 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.

12.7.3 GROUP BY with Hidden Fields

MySQL has extended the use of GROUP BY. You can use columns or calculations in the SELECT expressions that don't appear in the GROUP BY part. This stands for any possible value for this group. You can use this to get better performance by avoiding sorting and grouping on unnecessary items. For example, you don't need to group on customer.name in the following query:

mysql> 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 if you don't run in ANSI mode.

Don't use this feature if the columns you omit from the GROUP BY part aren't unique in the group! You will get unpredictable results.

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 using MySQL Version 3.22 (or earlier) or if you are trying to follow SQL-99, you can't use expressions in GROUP BY or ORDER BY clauses. You can work around this limitation by using an alias for the expression:

mysql> SELECT id,FLOOR(value/100) AS val FROM tbl_name
    ->        GROUP BY id,val ORDER BY val;

In MySQL Version 3.23 you can do:

mysql> SELECT id,FLOOR(value/100) FROM tbl_name ORDER BY RAND();


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