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12 Functions and Operators

Expressions can be used at several points in SQL statements, such as in the ORDER BY or HAVING clauses of SELECT statements, in the WHERE clause of a SELECT, DELETE, or UPDATE statement, or in SET statements. Expressions can be written using literal values, column values, NULL, functions, and operators. This chapter describes the functions and operators that are allowed for writing expressions in MySQL.

An expression that contains NULL always produces a NULL value unless otherwise indicated in the documentation for a particular function or operator.

Note: By default, there must be no whitespace between a function name and the parenthesis following it. This helps the MySQL parser distinguish between function calls and references to tables or columns that happen to have the same name as a function. Spaces around function arguments are permitted, though.

You can tell the MySQL server to accept spaces after function names by starting it with the --sql-mode=IGNORE_SPACE option. Individual client programs can request this behavior by using the CLIENT_IGNORE_SPACE option for mysql_real_connect(). In either case, all function names will become reserved words. See section 5.2.2 The Server SQL Mode.

For the sake of brevity, most examples in this chapter display the output from the mysql program in abbreviated form. Instead of showing examples in this format:

mysql> SELECT MOD(29,9);
+-----------+
| mod(29,9) |
+-----------+
|         2 |
+-----------+
1 rows in set (0.00 sec)

This format is used instead:

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

12.1 Operators

12.1.1 Operator Precedence

Operator precedences are shown in the following list, from lowest precedence to the highest. Operators that are shown together on a line have the same precedence.

:=
||, OR, XOR
&&, AND
NOT
BETWEEN, CASE, WHEN, THEN, ELSE
=, <=>, >=, >, <=, <, <>, !=, IS, LIKE, REGEXP, IN
|
&
<<, >>
-, +
*, /, DIV, %, MOD
^
- (unary minus), ~ (unary bit inversion)
!
BINARY, COLLATE

The precedence shown for NOT is as of MySQL 5.0.2. For earlier versions, or from 5.0.2 on if the HIGH_NOT_PRECEDENCE SQL mode is enabled, the precedence of NOT is the same as that of the ! operator. See section 5.2.2 The Server SQL Mode.

12.1.2 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

12.1.3 Comparison Functions and Operators

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

Some of the functions in this section (such as LEAST() and GREATEST()) return values other than 1 (TRUE), 0 (FALSE), or NULL. However, the value they return is based on comparison operations performed as described by the following rules.

MySQL compares values using the following rules:

• If one or both arguments are NULL, the result of the comparison is NULL, except for the NULL-safe <=> equality comparison operator.
• If both arguments in a comparison operation are strings, they are compared as strings.
• If both arguments are integers, they are compared as integers.
• Hexadecimal values are treated as binary strings if not compared to a number.
• If one of the arguments is a TIMESTAMP or DATETIME column and the other argument is a constant, the constant is converted to a timestamp before the comparison is performed. This is done to be more ODBC-friendly. Note that this is not done for arguments in IN()! To be safe, always use complete datetime/date/time strings when doing comparisons.
• In all other cases, the arguments are compared as floating-point (real) numbers.

By default, string comparisons are not case sensitive and use the current character set (ISO-8859-1 Latin1 by default, which also works excellently for English).

To convert a value to a specific type for comparison purposes, you can use the CAST() function. String values can be converted to a different character set using CONVERT(). See section 12.7 Cast Functions and Operators.

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 an index on the column to quickly look up the value. If str_col is an indexed string column, the index cannot be used when performing the lookup in the following statement:

SELECT * FROM tbl_name WHERE str_col=1;

The reason for this is that there are many different strings that may convert to 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

<=>

NULL-safe equal. This operator performs an equality comparison like the = operator, but returns 1 rather than NULL if both operands are NULL, and 0 rather than NULL if one operand is NULL.

mysql> SELECT 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
        -> 1, 1, 0
mysql> SELECT 1 = 1, NULL = NULL, 1 = NULL;
        -> 1, NULL, NULL

<=> was added in MySQL 3.23.0.

<>

!=

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

IS boolean_value

IS NOT boolean_value

Tests whether a value against a boolean value, where boolean_value can be TRUE, FALSE, or UNKNOWN.

mysql> SELECT 1 IS TRUE, 0 IS FALSE, NULL IS UNKNOWN;
        -> 1, 1, 1
mysql> SELECT 1 IS NOT UNKNOWN, 0 IS NOT UNKNOWN, NULL IS NOT UNKNOWN;
        -> 1, 1, 0

IS [NOT] boolean_value syntax was added in MySQL 5.0.2.

IS NULL

IS NOT NULL

Tests 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 ODBC programs, MySQL supports the following extra features when using IS NULL:

• You can find the row that contains the most recent AUTO_INCREMENT value by issuing a statement of the following form immediately after generating the value:

  SELECT * FROM tbl_name WHERE auto_col IS NULL
  

  This behavior can be disabled by setting SQL_AUTO_IS_NULL=0. See section 13.5.3 SET Syntax.
• For DATE and DATETIME columns that are declared as NOT NULL, you can find the special date '0000-00-00' by using a statement like this:

  SELECT * FROM tbl_name WHERE date_column IS NULL
  

  This is needed to get some ODBC applications to work because ODBC doesn't support a '0000-00-00' date value.

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 described at the beginning of this section, but applied to all the three arguments. Note: Before MySQL 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

This is the same as NOT (expr BETWEEN min AND max).

COALESCE(value,...)

Returns the first non-NULL value in the list.

mysql> SELECT COALESCE(NULL,1);
        -> 1
mysql> SELECT COALESCE(NULL,NULL,NULL);
        -> NULL

COALESCE() was added in MySQL 3.23.3.

GREATEST(value1,value2,...)

With two or more arguments, returns the largest (maximum-valued) argument. The arguments are compared using the same rules as for LEAST().

mysql> SELECT GREATEST(2,0);
        -> 2
mysql> SELECT GREATEST(34.0,3.0,5.0,767.0);
        -> 767.0
mysql> SELECT GREATEST('B','A','C');
        -> 'C'

Before MySQL 3.22.5, you can use MAX() instead of GREATEST().

expr IN (value,...)

Returns 1 if expr is any of the values in the IN list, else returns 0. If all values are constants, they are evaluated according to the type of expr and sorted. The search for the item then is done using a binary search. This means IN is very quick if the IN value list consists entirely of constants. 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. To comply with the SQL standard, from MySQL 4.1 on 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 4.1 on, IN() syntax also is used to write certain types of subqueries. See section 13.1.8.3 Subqueries with ANY, IN, and SOME.

expr NOT IN (value,...)

This is the 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!

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

LEAST(value1,value2,...)

With two or more arguments, returns the smallest (minimum-valued) argument. The arguments are compared using the following rules.

• If the return value is used in an INTEGER context or all arguments are integer-valued, they are compared as integers.
• If the return value is used in a REAL context or all arguments are real-valued, they are compared as reals.
• If any argument is a case-sensitive string, the arguments are compared as case-sensitive strings.
• In other cases, the arguments are compared as case-insensitive strings.

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'

Before MySQL 3.22.5, you can use MIN() instead of LEAST(). Note that the preceding conversion rules can produce strange results in some borderline cases:

mysql> SELECT CAST(LEAST(3600, 9223372036854775808.0) as SIGNED);
        -> -9223372036854775808

This happens because MySQL reads 9223372036854775808.0 in an integer context. The integer representation is not good enough to hold the value, so it wraps to a signed integer.

12.1.4 Logical Operators

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

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. As of MySQL 4.0.5, the code has been re-engineered so that the result is always as prescribed by the SQL standards while still using the optimization wherever possible.

OR

||

Logical OR. When both operands are non-NULL, the result is 1 if any operand is non-zero, and 0 otherwise. With a NULL operand, the result is 1 if the other operand is non-zero, and NULL otherwise. If both operands are NULL, the result is NULL.

mysql> SELECT 1 || 1;
        -> 1
mysql> SELECT 1 || 0;
        -> 1
mysql> SELECT 0 || 0;
        -> 0
mysql> SELECT 0 || NULL;
        -> NULL
mysql> SELECT 1 || NULL;
        -> 1

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 MySQL 4.0.2.

12.2 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 that is true. If there was no matching result value, the result after ELSE is returned, or NULL if there is no ELSE part.

mysql> SELECT CASE 1 WHEN 1 THEN 'one'
    ->     WHEN 2 THEN 'two' ELSE 'more' END;
        -> 'one'
mysql> SELECT CASE WHEN 1>0 THEN 'true' ELSE 'false' END;
        -> 'true'
mysql> SELECT CASE BINARY 'B'
    ->     WHEN 'a' THEN 1 WHEN 'b' THEN 2 END;
        -> NULL

The 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). CASE was added in MySQL 3.23.3.

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 only one of expr2 or expr3 is explicitly NULL, the result type of the IF() function is the type of non-NULL expression. (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 shown, IF(0.1) returns 0 because 0.1 is converted to an integer value, resulting in a test of IF(0). This may not be what you expect. In the second case, the comparison tests the original floating-point value to see whether it is non-zero. The result of the comparison is used as an integer. The default return type of IF() (which may matter when it is stored into a temporary table) is calculated in MySQL 3.23 as follows:

Expression	Return Value
expr2 or expr3 returns a string	string
expr2 or expr3 returns a floating-point value	floating-point
expr2 or expr3 returns an integer	integer

If expr2 and expr3 are strings, the result is case sensitive if either string is case sensitive (starting from MySQL 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 from earlier MySQL versions is 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 tmp SELECT IFNULL(1,'test') AS test;

As of MySQL 4.0.6, the type for the test column is CHAR(4), whereas in earlier versions the type would be BIGINT.

NULLIF(expr1,expr2)

Returns NULL if expr1 = expr2 is true, else returns expr1. This is the same as CASE WHEN expr1 = expr2 THEN NULL ELSE expr1 END.

mysql> SELECT NULLIF(1,1);
        -> NULL
mysql> SELECT NULLIF(1,2);
        -> 1

Note that MySQL evaluates expr1 twice if the arguments are not equal. NULLIF() was added in MySQL 3.23.15.

12.3 String Functions

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

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

ASCII(str)

Returns the numeric value of the leftmost character of the string str. Returns 0 if str is the empty string. Returns NULL if str is NULL. ASCII() works for characters with numeric values from 0 to 255.

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

BIT_LENGTH() was added in MySQL 4.0.2.

CHAR(N,...)

CHAR() interprets the arguments as integers and returns a string consisting of the characters given by the code values of those integers. NULL values are skipped.

mysql> SELECT CHAR(77,121,83,81,'76');
        -> 'MySQL'
mysql> SELECT CHAR(77,77.3,'77.3');
        -> 'MMM'

CHAR_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. This function requires MySQL to have been compiled with a compression library such as zlib. Otherwise, the return value is always NULL. The compressed string can be uncompressed with UNCOMPRESS().

mysql> SELECT LENGTH(COMPRESS(REPEAT('a',1000)));
        -> 21
mysql> SELECT LENGTH(COMPRESS(''));
        -> 0
mysql> SELECT LENGTH(COMPRESS('a'));
        -> 13
mysql> SELECT LENGTH(COMPRESS(REPEAT('a',16)));
        -> 15

The compressed string contents are stored the following way:

• Empty strings are stored as empty strings.
• Non-empty strings are stored as a four-byte length of the uncompressed string (low byte first), followed by the compressed string. If the string ends with space, an extra `.' character is added to avoid problems with endspace trimming should the result be stored in a CHAR or VARCHAR column. (Use of CHAR or VARCHAR to store compressed strings is not recommended. It is better to use a BLOB column instead.)

COMPRESS() was added in MySQL 4.1.1.

CONCAT(str1,str2,...)

Returns the string that results from concatenating the arguments. Returns NULL if any argument is NULL. May have one or more arguments. If all arguments are non-binary strings, the result is a non-binary string. If the arguments include any binary strings, the result is a binary string. A numeric argument is converted to its equivalent binary string form.

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 the value bits, you get an on string and for every reset bit you get an off string. Bits in bits are examined from right to left (from low-order to high-order bits). Strings are added to the result from left to right, separated by the separator string (default `,'). The number of bits examined is given by number_of_bits (default 64).

mysql> SELECT EXPORT_SET(5,'Y','N',',',4);
        -> 'Y,N,Y,N'
mysql> SELECT EXPORT_SET(6,'1','0',',',10);
        -> '0,1,1,0,0,0,0,0,0,0'

FIELD(str,str1,str2,str3,...)

Returns the index of str in the str1, str2, str3, ... list. Returns 0 if str is not found. If str is NULL, the return value is 0 because NULL fails equality comparison with any value. FIELD() is the complement of ELT().

mysql> SELECT FIELD('ej', 'Hej', 'ej', 'Heja', 'hej', 'foo');
        -> 2
mysql> SELECT FIELD('fo', 'Hej', 'ej', 'Heja', 'hej', 'foo');
        -> 0

FIND_IN_SET(str,strlist)

Returns a value 1 to N if the string str is in the string list strlist consisting of N substrings. A string list is a string composed of substrings separated by `,' characters. If the first argument is a constant string and the second is a column of type SET, the FIND_IN_SET() function is optimized to use bit arithmetic. Returns 0 if str is not in strlist or if strlist is the empty string. Returns NULL if either argument is NULL. This function will not work properly if the first argument contains a comma (`,') character.

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). From MySQL 4.0.1 and up, 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 0x616263;
        -> 'abc'
mysql> SELECT HEX('abc');
        -> 616263

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. Returns the original string if pos is not within the length of the string. Replaces the rest of the string from position pos is len is not within the length of the rest of the string. Returns NULL if any argument is null.

mysql> SELECT INSERT('Quadratic', 3, 4, 'What');
        -> 'QuWhattic'
mysql> SELECT INSERT('Quadratic', -1, 4, 'What');
        -> 'Quadratic'
mysql> SELECT INSERT('Quadratic', 3, 100, 'What');
        -> 'QuWhat'

This function is multi-byte safe.

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. For 4.0 on, it is case sensitive only 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 located 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 bytes. If the file doesn't exist or cannot be read because one of the preceding conditions is not satisfied, the function returns NULL.

mysql> UPDATE tbl_name
           SET blob_column=LOAD_FILE('/tmp/picture')
           WHERE id=1;

Before MySQL 3.23, you must read the file inside your application and create an INSERT statement to update the database with the file contents. If you are using the MySQL++ library, one way to do this can be found in the MySQL++ manual, available at http://dev.mysql.com/doc/.

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. For 4.0 on, it is case sensitive only 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'
mysql> SELECT LPAD('hi',1,'??');
        -> 'h'

LTRIM(str)

Returns the string str with leading space characters removed.

mysql> SELECT LTRIM('  barbar');
        -> 'barbar'

This function is multi-byte safe.

MAKE_SET(bits,str1,str2,...)

Returns a set value (a string containing substrings separated by `,' characters) consisting of the strings that have the corresponding bit in bits set. str1 corresponds to bit 0, str2 to bit 1, and so on. NULL values in str1, str2, ... are not appended to the result.

mysql> SELECT MAKE_SET(1,'a','b','c');
        -> 'a'
mysql> SELECT MAKE_SET(1 | 4,'hello','nice','world');
        -> 'hello,world'
mysql> SELECT MAKE_SET(1 | 4,'hello','nice',NULL,'world');
        -> 'hello'
mysql> SELECT MAKE_SET(0,'a','b','c');
        -> ''

MID(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 (BIGINT)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 numeric values of its constituent bytes using this formula:

  (1st byte code)
+ (2nd byte code * 256)
+ (3rd byte code * 256^2) ...

If the leftmost character is not a multi-byte character, ORD() returns the same value as the ASCII() function.

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 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???'
mysql> SELECT RPAD('hi',1,'?');
        -> 'h'

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 four characters long, but the SOUNDEX() function returns an arbitrarily long string. You can use SUBSTRING() on the result to get a standard soundex string. All non-alphabetic characters are ignored in the given string. All international alphabetic 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 discards vowels first and then duplicates, whereas the enhanced version discards duplicates first and then vowels.

expr1 SOUNDS LIKE expr2

This is the same as SOUNDEX(expr1) = SOUNDEX(expr2). It is available only in MySQL 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 standard SQL 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)

TRIM(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 optional and 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. If the argument is not a compressed value, the result is NULL. This function requires MySQL to have been compiled with a compression library such as zlib. Otherwise, the return value is always NULL.

mysql> SELECT UNCOMPRESS(COMPRESS('any string'));
        -> 'any string'
mysql> SELECT UNCOMPRESS('any string');
        -> NULL

UNCOMPRESS() was added in MySQL 4.1.1.

UNCOMPRESSED_LENGTH(compressed_string)

Returns the length of a compressed string before compression.

mysql> SELECT UNCOMPRESSED_LENGTH(COMPRESS(REPEAT('a',30)));
        -> 30

UNCOMPRESSED_LENGTH() was added in MySQL 4.1.1.

UNHEX(str)

Does the opposite of HEX(str). That is, it interprets each pair of hexadecimal digits in the argument as a number and converts it to the character represented by the number. The resulting characters are returned as a binary string.

mysql> SELECT UNHEX('4D7953514C');
        -> 'MySQL'
mysql> SELECT 0x4D7953514C;
        -> 'MySQL'
mysql> SELECT UNHEX(HEX('string'));
        -> 'string'
mysql> SELECT HEX(UNHEX('1267'));
        -> '1267'

UNHEX() was added in MySQL 4.1.2.

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.

12.3.1 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, use the CAST() or CONCAT() function:

mysql> SELECT 38.8, CAST(38.8 AS CHAR);
        -> 38.8, '38.8'
mysql> SELECT 38.8, CONCAT(38.8);
        -> 38.8, '38.8'

CAST() is preferable, but it is unavailable before MySQL 4.0.2.

If a string function is given a binary string as an argument, the resulting string is also a binary string. A number converted to a string is treated as a binary string. This affects only comparisons.

Normally, if any expression in a string comparison is case sensitive, the comparison is performed in case-sensitive fashion.

expr LIKE pat [ESCAPE 'escape-char']

Pattern matching using SQL simple regular expression comparison. Returns 1 (TRUE) or 0 (FALSE). If either expr or pat is NULL, the result is NULL. With LIKE you can use the following two wildcard characters in the pattern:

Character	Description
%	Matches any number of characters, even zero characters
_	Matches exactly one character

mysql> SELECT 'David!' LIKE 'David_';
        -> 1
mysql> SELECT 'David!' LIKE '%D%v%';
        -> 1

To test for literal instances of a wildcard character, precede 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

In MySQL, LIKE is allowed on numeric expressions. (This is an extension to the standard SQL LIKE.)

mysql> SELECT 10 LIKE '1%';
        -> 1

Note: Because MySQL uses the C escape syntax in strings (for example, `\n' to represent newline), 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).

expr NOT LIKE pat [ESCAPE 'escape-char']

This is the same as NOT (expr LIKE pat [ESCAPE 'escape-char']).

expr NOT REGEXP pat

expr NOT RLIKE pat

This is the same as NOT (expr REGEXP pat).

expr REGEXP pat

expr RLIKE pat

Performs a pattern match of a string expression expr against a pattern pat. The pattern can be an extended regular expression. The syntax for regular expressions is discussed in section G MySQL Regular Expressions. Returns 1 if expr matches pat, otherwise returns 0. If either expr or pat is NULL, the result is NULL. RLIKE is a synonym for REGEXP, provided for mSQL compatibility. Note: Because MySQL uses the C escape syntax in strings (for example, `\n' to represent newline), you must double any `\' that you use in your REGEXP strings. As of MySQL 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. However, these operators are not multi-byte safe.

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.

12.4 Numeric Functions

12.4.1 Arithmetic Operators

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 12.7 Cast Functions and Operators.

+

Addition:

mysql> SELECT 3+5;
        -> 8

-

Subtraction:

mysql> SELECT 3-5;
        -> -2

-

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!

*

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!

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.

12.4.2 Mathematical Functions

All mathematical functions return NULL in case of an error.

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

Note that the return value is converted to a BIGINT! The CEIL() alias was added in MySQL 4.0.6.

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

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!

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 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 arbitrary base B.

mysql> SELECT LOG(2,65536);
        -> 16.000000
mysql> SELECT LOG(1,100);
        -> NULL

The arbitrary base option was added in MySQL 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 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)

N % M

N MOD M

Modulo operation. Returns the remainder of N divided by M.

mysql> SELECT MOD(234, 10);
        -> 4
mysql> SELECT 253 % 7;
        -> 1
mysql> SELECT MOD(29,9);
        -> 2
mysql> SELECT 29 MOD 9;
        -> 2

This function is safe to use with BIGINT values. The N MOD M syntax works only as of MySQL 4.1. As of MySQL 4.1.7, MOD() works on values with a fractional part and returns the exact remainder after division:

mysql> SELECT MOD(34.5,3);
        -> 1.5

Before MySQL 4.1.7, MOD() rounds arguments with a fractional value to integers and returns an integer result:

mysql> SELECT MOD(34.5,3);
        -> 2

PI()

Returns the value of PI. The default number of decimals displayed is five, but MySQL internally uses the full double-precision value 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 from 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. As of MySQL 3.23, you can retrieve rows in random order like this:

mysql> SELECT * FROM tbl_name ORDER BY RAND();

ORDER BY RAND() combined with LIMIT is useful for selecting a random sample of a set of rows:

mysql> SELECT * FROM table1, table2 WHERE a=b AND c<d
    -> ORDER BY RAND() LIMIT 1000;

Note that RAND() in a WHERE clause is re-evaluated every time the WHERE is executed. RAND() is not meant to be a perfect random generator, but instead 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, returns X rounded to D decimals. If D is negative, the integer part of the number is zeroed out.

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. Different implementations round to the nearest even number, always up, always down, or always toward zero. If you need one kind of rounding, you should use a well-defined function such as TRUNCATE() or FLOOR() instead.

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. If D is negative, the integer part of the number is zeroed out.

mysql> SELECT TRUNCATE(1.223,1);
        -> 1.2
mysql> SELECT TRUNCATE(1.999,1);
        -> 1.9
mysql> SELECT TRUNCATE(1.999,0);
        -> 1
mysql> SELECT TRUNCATE(-1.999,1);
        -> -1.9
mysql> SELECT TRUNCATE(122,-2);
       -> 100

Starting from MySQL 3.23.51, all numbers are rounded toward zero. Note that decimal numbers are normally not stored as exact numbers in computers, but as double-precision values, so you may be surprised by the following result:

mysql> SELECT TRUNCATE(10.28*100,0);
       -> 1027

This happens because 10.28 is actually stored as something like 10.2799999999999999.

12.5 Date and Time Functions

This section describes the functions that can be used to manipulate temporal values. See section 11.3 Date and Time Types for a description of the range of values each date and time type has and the valid formats in which values may be specified.

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 DATE_SUB(CURDATE(),INTERVAL 30 DAY) <= date_col;

Note that the query also will 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 to any of their synonyms.

Beginning with MySQL 4.1.3, the CURRENT_TIMESTAMP(), CURRENT_TIME(), CURRENT_DATE(), and FROM_UNIXTIME() functions return values in the connection's current time zone, which is available as the value of the time_zone system variable. Also, UNIX_TIMESTAMP() assumes that its argument is a datetime value in the current time zone. See section 5.8.8 MySQL Server Time Zone Support.

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(). For information on the INTERVAL argument, see the discussion for DATE_ADD().

mysql> SELECT DATE_ADD('1998-01-02', INTERVAL 31 DAY);
        -> '1998-02-02'
mysql> SELECT ADDDATE('1998-01-02', INTERVAL 31 DAY);
        -> '1998-02-02'

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 time or datetime expression, and expr2 is a time expression.

mysql> SELECT ADDTIME('1997-12-31 23:59:59.999999',
    ->                '1 1:1:1.000002');
        -> '1998-01-02 01:01:01.000001'
mysql> SELECT ADDTIME('01:00:00.999999', '02:00:00.999998');
        -> '03:00:01.999997'

ADDTIME() was added in MySQL 4.1.1.

CONVERT_TZ(dt,from_tz,to_tz)

CONVERT_TZ() converts a datetime value dt from time zone given by from_tz to the time zone given by to_tz and returns the resulting value. Time zones may be specified as described in section 5.8.8 MySQL Server Time Zone Support. This function returns NULL if the arguments are invalid. If the value falls out of the supported range of the TIMESTAMP type when converted fom from_tz to UTC, no conversion occurs. The TIMESTAMP range is described at section 11.1.2 Overview of Date and Time Types.

mysql> SELECT CONVERT_TZ('2004-01-01 12:00:00','GMT','MET');
        -> '2004-01-01 13:00:00'
mysql> SELECT CONVERT_TZ('2004-01-01 12:00:00','+00:00','-07:00');
        -> '2004-01-01 05:00:00'

To use named time zones such as 'MET' or 'Europe/Moscow', the time zone tables must be properly set up. See section 5.8.8 MySQL Server Time Zone Support for instructions. CONVERT_TZ() was added in MySQL 4.1.3.

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('1997-11-30 23:59:59','1997-12-31');
        -> -31

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. 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 INTERVAL keyword and the type specifier are not case sensitive. 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. As of MySQL 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.)

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 that 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. 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'

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, ...)
%d	Day of the month, numeric (00..31)
%e	Day of the month, numeric (0..31)
%f	Microseconds (000000..999999)
%H	Hour (00..23)
%h	Hour (01..12)
%I	Hour (01..12)
%i	Minutes, numeric (00..59)
%j	Day of year (001..366)
%k	Hour (0..23)
%l	Hour (1..12)
%M	Month name (January..December)
%m	Month, numeric (00..12)
%p	AM or PM
%r	Time, 12-hour (hh:mm:ss followed by AM or PM)
%S	Seconds (00..59)
%s	Seconds (00..59)
%T	Time, 24-hour (hh:mm:ss)
%U	Week (00..53), where Sunday is the first day of the week
%u	Week (00..53), where Monday is the first day of the week
%V	Week (01..53), where Sunday is the first day of the week; used with %X
%v	Week (01..53), where Monday is the first day of the week; used with %x
%W	Weekday name (Sunday..Saturday)
%w	Day of the week (0=Sunday..6=Saturday)
%X	Year for the week where Sunday is the first day of the week, numeric, four digits; used with %V
%x	Year for the week, where Monday is the first day of the week, numeric, four digits; used with %v
%Y	Year, numeric, four digits
%y	Year, numeric, two digits
%%	A literal `%'.

All other characters are copied to the result without interpretation. The %v, %V, %x, and %X format specifiers are available as of MySQL 3.23.8. %f is available as of MySQL 4.1.1. As of MySQL 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

EXTRACT() was added in MySQL 3.23.0.

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 does not 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|DATETIME, 'EUR'|'USA'|'JIS'|'ISO'|'INTERNAL')

Returns a format string. This function is useful in combination with the DATE_FORMAT() and the STR_TO_DATE() functions. The 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(DATETIME,'USA')	'%Y-%m-%d-%H.%i.%s'
GET_FORMAT(DATETIME,'JIS')	'%Y-%m-%d %H:%i:%s'
GET_FORMAT(DATETIME,'ISO')	'%Y-%m-%d %H:%i:%s'
GET_FORMAT(DATETIME,'EUR')	'%Y-%m-%d-%H.%i.%s'
GET_FORMAT(DATETIME,'INTERNAL')	'%Y%m%d%H%i%s'
GET_FORMAT(TIME,'USA')	'%h:%i:%s %p'
GET_FORMAT(TIME,'JIS')	'%H:%i:%s'
GET_FORMAT(TIME,'ISO')	'%H:%i:%s'
GET_FORMAT(TIME,'EUR')	'%H.%i.%S'
GET_FORMAT(TIME,'INTERNAL')	'%H%i%s'

ISO format is ISO 9075, not ISO 8601. As of MySQL 4.1.4, TIMESTAMP can also be used; GET_FORMAT() returns the same values as for DATETIME.

mysql> SELECT DATE_FORMAT('2003-10-03',GET_FORMAT(DATE,'EUR'));
        -> '03.10.2003'
mysql> SELECT STR_TO_DATE('10.31.2003',GET_FORMAT(DATE,'USA'));
        -> 2003-10-31

GET_FORMAT() is available as of MySQL 4.1.1. See section 13.5.3 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');
        -> '2003-02-28'
mysql> SELECT LAST_DAY('2004-02-05');
        -> '2004-02-29'
mysql> SELECT LAST_DAY('2004-01-01 01:01:01');
        -> '2004-01-31'
mysql> SELECT LAST_DAY('2003-03-32');
        -> NULL

LAST_DAY() is available as of MySQL 4.1.1.

LOCALTIME

LOCALTIME()

LOCALTIME and LOCALTIME() are synonyms for NOW(). They were added in MySQL 4.0.6.

LOCALTIMESTAMP

LOCALTIMESTAMP()

LOCALTIMESTAMP and LOCALTIMESTAMP() are synonyms for NOW(). They were added in MySQL 4.0.6.

MAKEDATE(year,dayofyear)

Returns a date, given year and day-of-year values. dayofyear must be greater than 0 or the result will be 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 full 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. STR_TO_DATE() returns a DATETIME value if the format string contains both date and time parts, or a DATE or TIME value if the string contains only date or time parts. The date, time, or datetime values contained in str should be given in the format indicated by format. For the specifiers that can be used in format, see the 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',
    ->