MySQL Reference Manual for version 3.23.58.: 6.3 Functions for Use in SELECT and WHERE Clauses

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6.3 Functions for Use in `SELECT` and `WHERE` Clauses

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 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

6.3.1 Non-Type-Specific Operators and Functions

6.3.1.1 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

6.3.1.2 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:

If one or both arguments are NULL, the result of the comparison is NULL, except for the <=> 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.
In all other cases, the arguments are compared as floating-point (real) numbers.

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).

If you are comparing case-insensitive strings with any of the standard operators (=, <>..., but not LIKE) trailing whitespace (spaces, tabs and newlines) will be ignored.

mysql> SELECT "a" ="A \n";
        -> 1

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

=

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:

You can find the last inserted row with:
SELECT * FROM tbl_name WHERE auto_col IS NULL
This can be disabled by setting SQL_AUTO_IS_NULL=0. See section SET Syntax.
For NOT NULL DATE and DATETIME columns you can find the special date 0000-00-00 by using:
SELECT * FROM tbl_name WHERE date_column IS NULL
This is needed to get some ODBC applications to work (as ODBC doesn't support a 0000-00-00 date)

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.

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

6.3.1.3 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 0s. 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 optimisation 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.

 example_for_help_topic XOR
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.

6.3.1.4 Control Flow Functions

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 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.

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 explicitely NULL then the result type of the IF() function is the type of the not NULL column. (This behaviour 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)

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).

6.3.2 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 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

6.3.2.1 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 case-insensitive 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.

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

Same as NOT (expr LIKE pat [ESCAPE 'escape-char']).

expr SOUNDS LIKE expr

Same as SOUNDEX(expr)=SOUNDEX(expr) (available only in version 4.1 or later).

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 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 case-insensitive 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.

expr NOT REGEXP pat

expr NOT RLIKE pat

Same as NOT (expr REGEXP pat).

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

MATCH (col1,col2,...) AGAINST (expr)

MATCH (col1,col2,...) AGAINST (expr IN BOOLEAN MODE)

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. For details and usage examples, see MySQL Full-text Search.

6.3.2.2 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 Cast Functions. BINARY was introduced in MySQL Version 3.23.0.

Note that in some context MySQL will not be able to use the index efficiently when you cast an indexed column to BINARY.

If you want to compare a blob case-insensitively you can always convert the blob to upper case before doing the comparison:

SELECT 'A' LIKE UPPER(blob_col) FROM table_name;

We plan to soon introduce casting between different character sets to make string comparison even more flexible.

6.3.3 Numeric Functions

6.3.3.1 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 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!

6.3.3.2 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.

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

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 only works in MySQL 4.1

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!

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!

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 behaviour of ROUND() when the argument is half way 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 like TRUNCATE() or FLOOR() instead.

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

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

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

SQRT(X)

Returns the non-negative square root of X:

mysql> SELECT SQRT(4);
        -> 2.000000
mysql> SELECT SQRT(20);
        -> 4.472136

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

COS(X)

Returns the cosine of X, where X is given in radians:

mysql> SELECT COS(PI());
        -> -1.000000

SIN(X)

Returns the sine of X, where X is given in radians:

mysql> SELECT SIN(PI());
        -> 0.000000

TAN(X)

Returns the tangent of X, where X is given in radians:

mysql> SELECT TAN(PI()+1);
        -> 1.557408

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

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.

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.

LEAST(X,Y,...)

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"

In MySQL versions prior to Version 3.22.5, you can use MIN() instead of LEAST.

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.

DEGREES(X)

Returns the argument X, converted from radians to degrees:

mysql> SELECT DEGREES(PI());
        -> 180.000000

RADIANS(X)

Returns the argument X, converted from degrees to radians:

mysql> SELECT RADIANS(90);
        -> 1.570796

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, then the whole part of the number is zeroed out:

mysql> SELECT TRUNCATE(122,-2);
       -> 100

Note that as decimal numbers are normally not stored as exact numbers in computers, but as double-precision values, 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.

6.3.4 Date and Time Functions

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

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.

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.

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.

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

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

DAYOFMONTH(date)

Returns the day of the month for date, in the range 1 to 31:

mysql> SELECT DAYOFMONTH('1998-02-03');
        -> 3

DAY(date)

DAY() is a synonym for DAYOFMONTH(). It is available as of MySQL 4.1.1.

DAYOFYEAR(date)

Returns the day of the year for date, in the range 1 to 366:

mysql> SELECT DAYOFYEAR('1998-02-03');
        -> 34

MONTH(date)

Returns the month for date, in the range 1 to 12:

mysql> SELECT MONTH('1998-02-03');
        -> 2

DAYNAME(date)

Returns the name of the weekday for date:

mysql> SELECT DAYNAME('1998-02-05');
        -> 'Thursday'

MONTHNAME(date)

Returns the name of the month for date:

mysql> SELECT MONTHNAME('1998-02-05');
        -> 'February'

QUARTER(date)

Returns the quarter of the year for date, in the range 1 to 4:

mysql> SELECT QUARTER('98-04-01');
        -> 2

WEEK(date)

WEEK(date,start)

With a single argument, returns the week for date, in the range 0 to 53 (yes, there may be the beginnings of a week 53), for locations where Sunday is the first day of the week. 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.

The following table demonstrates how the start argument works:

Value	Meaning
`0`	Week starts on Sunday; return value range is `0` to `53`
`1`	Week starts on Monday; return value range is `0` to `53`
`2`	Week starts on Sunday; return value range is `1` to `53`
`3`	Week starts on Monday; return value range is `1` to `53` (ISO 8601)

The start value of 3 can be used as of MySQL 4.0.5.

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

For MySQL 3.23 and 4.0, the default value for the start argument is 0. In MySQL 4.1, you can control the default value of the start argument by using the default_week_format variable. The syntax for setting default_week_format is:

SET [SESSION | GLOBAL] default_week_format = {0|1|2|3};

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 or 3 as the optional start 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 or 3 as the optional start 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'

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.

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

MINUTE(time)

Returns the minute for time, in the range 0 to 59:

mysql> SELECT MINUTE('98-02-03 10:05:03');
        -> 5

SECOND(time)

Returns the second for time, in the range 0 to 59:

mysql> SELECT SECOND('10:05:03');
        -> 3

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.

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

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
`SECOND`	`SECONDS`
`MINUTE`	`MINUTES`
`HOUR`	`HOURS`
`DAY`	`DAYS`
`MONTH`	`MONTHS`
`YEAR`	`YEARS`
`MINUTE_SECOND`	`'MINUTES:SECONDS'`
`HOUR_MINUTE`	`'HOURS:MINUTES'`
`DAY_HOUR`	`'DAYS HOURS'`
`YEAR_MONTH`	`'YEARS-MONTHS'`
`HOUR_SECOND`	`'HOURS:MINUTES:SECONDS'`
`DAY_MINUTE`	`'DAYS HOURS:MINUTES'`
`DAY_SECOND`	`'DAYS HOURS:MINUTES:SECONDS'`
`DAY_MICROSECOND`	`'DAYS.MICROSECONDS'`
`HOUR_MICROSECOND`	`'HOURS.MICROSECONDS'`
`MINUTE_MICROSECOND`	`'MINUTES.MICROSECONDS'`
`SECOND_MICROSECOND`	`'SECONDS.MICROSECONDS'`
`MICROSECOND`	`'MICROSECONDS'`

The type values DAY_MICROSECOND, HOUR_MICROSECOND, MINUTE_MICROSECOND, SECOND_MICROSECOND, and MICROSECOND are allowed as of MySQL 4.1.1.

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.

ADDDATE(date,INTERVAL expr type)

SUBDATE(date,INTERVAL expr type)

ADDDATE(expr,days)

SUBDATE(expr,days)

When invoked with the INTERVAL form of the second argument, ADDDATE() and SUBDATE() are synonyms for DATE_ADD() and 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'
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 added to or subtracted from expr.

mysql> SELECT ADDDATE('1998-01-02', 31);
        -> '1998-02-02'
mysql> SELECT SUBDATE('1998-01-02 12:00:00', 31);
        -> '1997-12-02 12:00:00'

ADDTIME(expr,expr2)

SUBTIME(expr,expr2)

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

[Rest of description to be added here]

NEED EXAMPLE

ADDTIME() and SUBTIME() were added in MySQL 4.1.1.

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

DATEDIFF(ARGUMENTS)

TIMEDIFF(ARGUMENTS)

[Rest of description to be added here]

NEED EXAMPLE

DATEDIFF() and TIMEDIFF() were added in MySQL 4.1.1.

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.

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.

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
`%M`	Month name (`January`..`December`)
`%W`	Weekday name (`Sunday`..`Saturday`)
`%D`	Day of the month with English suffix (`0th`, `1st`, `2nd`, `3rd`, etc.)
`%Y`	Year, numeric, 4 digits
`%y`	Year, numeric, 2 digits
`%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`
`%a`	Abbreviated weekday name (`Sun`..`Sat`)
`%d`	Day of the month, numeric (`00`..`31`)
`%e`	Day of the month, numeric (`0`..`31`)
`%m`	Month, numeric (`00`..`12`)
`%c`	Month, numeric (`0`..`12`)
`%b`	Abbreviated month name (`Jan`..`Dec`)
`%j`	Day of year (`001`..`366`)
`%H`	Hour (`00`..`23`)
`%k`	Hour (`0`..`23`)
`%h`	Hour (`01`..`12`)
`%I`	Hour (`01`..`12`)
`%l`	Hour (`1`..`12`)
`%i`	Minutes, numeric (`00`..`59`)
`%r`	Time, 12-hour (`hh:mm:ss` followed by `AM` or `PM`)
`%T`	Time, 24-hour (`hh:mm:ss`)
`%S`	Seconds (`00`..`59`)
`%s`	Seconds (`00`..`59`)
`%f`	Microseconds (`000000`..`999999`)
`%p`	`AM` or `PM`
`%w`	Day of the week (`0`=Sunday..`6`=Saturday)
`%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`
`%%`	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'

TIME_FORMAT(time,format)

This is used like the DATE_FORMAT() function above, 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'

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.

CURDATE()

CURRENT_DATE

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

CURTIME()

CURRENT_TIME

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

NOW()

SYSDATE()

CURRENT_TIMESTAMP

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

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 may want to cast the result to signed integers. See section Cast Functions.

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'

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

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

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()

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()

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.

6.3.5 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:

BINARY
CHAR
DATE
DATETIME
SIGNED {INTEGER}
TIME
UNSIGNED {INTEGER}

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 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 will automatically 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);

6.3.6 Other Functions

6.3.6.1 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