Chapter 12 Functions and Operators

By default, || is a logical OR operator. With PIPES_AS_CONCAT enabled, || is string concatenation, with a precedence between ^ and the unary operators.

By default, ! has a higher precedence than NOT. With HIGH_NOT_PRECEDENCE enabled, ! and NOT have the same precedence.

=

Equal:

mysql> SELECT 1 = 0;
        -> 0
mysql> SELECT '0' = 0;
        -> 1
mysql> SELECT '0.0' = 0;
        -> 1
mysql> SELECT '0.01' = 0;
        -> 0
mysql> SELECT '.01' = 0.01;
        -> 1

For row comparisons, (a, b) = (x, y) is equivalent to:

(a = x) AND (b = y)

<=>

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

The <=> operator is equivalent to the standard SQL IS NOT DISTINCT FROM operator.

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

For row comparisons, (a, b) <=> (x, y) is equivalent to:

(a <=> x) AND (b <=> y)

<>, !=

Not equal:

mysql> SELECT '.01' <> '0.01';
        -> 1
mysql> SELECT .01 <> '0.01';
        -> 0
mysql> SELECT 'zapp' <> 'zappp';
        -> 1

For row comparisons, (a, b) <> (x, y) and (a, b) != (x, y) are equivalent to:

(a <> x) OR (b <> y)

<=

Less than or equal:

mysql> SELECT 0.1 <= 2;
        -> 1

For row comparisons, (a, b) <= (x, y) is equivalent to:

(a < x) OR ((a = x) AND (b <= y))

<

Less than:

mysql> SELECT 2 < 2;
        -> 0

For row comparisons, (a, b) < (x, y) is equivalent to:

(a < x) OR ((a = x) AND (b < y))

>=

Greater than or equal:

mysql> SELECT 2 >= 2;
        -> 1

For row comparisons, (a, b) >= (x, y) is equivalent to:

(a > x) OR ((a = x) AND (b >= y))

>

Greater than:

mysql> SELECT 2 > 2;
        -> 0

For row comparisons, (a, b) > (x, y) is equivalent to:

(a > x) OR ((a = x) AND (b > y))

IS boolean_value

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

mysql> SELECT 1 IS TRUE, 0 IS FALSE, NULL IS UNKNOWN;
        -> 1, 1, 1

IS NOT boolean_value

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

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

IS NULL

Tests whether a value is NULL.

mysql> SELECT 1 IS NULL, 0 IS NULL, NULL IS NULL;
        -> 0, 0, 1

To work well with ODBC programs, MySQL supports the following extra features when using IS NULL:

IS NOT NULL

Tests whether a value is not NULL.

mysql> SELECT 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL;
        -> 1, 1, 0

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 in Section 12.2, “Type Conversion in Expression Evaluation”, but applied to all the three arguments.

mysql> SELECT 2 BETWEEN 1 AND 3, 2 BETWEEN 3 and 1;
        -> 1, 0
mysql> SELECT 1 BETWEEN 2 AND 3;
        -> 0
mysql> SELECT 'b' BETWEEN 'a' AND 'c';
        -> 1
mysql> SELECT 2 BETWEEN 2 AND '3';
        -> 1
mysql> SELECT 2 BETWEEN 2 AND 'x-3';
        -> 0

For best results when using BETWEEN with date or time values, use CAST() to explicitly convert the values to the desired data type. Examples: If you compare a DATETIME to two DATE values, convert the DATE values to DATETIME values. If you use a string constant such as '2001-1-1' in a comparison to a DATE, cast the string to a DATE.

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, or NULL if there are no non-NULL values.

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

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'

GREATEST() returns NULL if any argument is NULL.

expr IN (value,...)

Returns 1 if expr is equal to any of the values in the IN list, else returns 0. If all values are constants, they are evaluated according to the type of expr and sorted. The search for the item then is done using a binary search. This means IN is very quick if the IN value list consists entirely of constants. Otherwise, type conversion takes place according to the rules described in Section 12.2, “Type Conversion in Expression Evaluation”, but applied to all the arguments.

mysql> SELECT 2 IN (0,3,5,7);
        -> 0
mysql> SELECT 'wefwf' IN ('wee','wefwf','weg');
        -> 1

You should never mix quoted and unquoted values in an IN list because the comparison rules for quoted values (such as strings) and unquoted values (such as numbers) differ. Mixing types may therefore lead to inconsistent results. For example, do not write an IN expression like this:

SELECT val1 FROM tbl1 WHERE val1 IN (1,2,'a');

Instead, write it like this:

SELECT val1 FROM tbl1 WHERE val1 IN ('1','2','a');

The number of values in the IN list is only limited by the max_allowed_packet value.

To comply with the SQL standard, IN returns NULL not only if the expression on the left hand side is NULL, but also if no match is found in the list and one of the expressions in the list is NULL.

IN() syntax can also be used to write certain types of subqueries. See Section 13.2.10.3, “Subqueries with ANY, IN, or 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

ISNULL() can be used instead of = to test whether a value is NULL. (Comparing a value to NULL using = always yields false.)

The ISNULL() function shares some special behaviors with the IS NULL comparison operator. See the description of IS NULL.

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:

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

Note that the preceding conversion rules can produce strange results in some borderline cases:

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

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

NOT, !

Logical NOT. Evaluates to 1 if the operand is 0, to 0 if the operand is nonzero, and NOT NULL returns NULL.

mysql> SELECT NOT 10;
        -> 0
mysql> SELECT NOT 0;
        -> 1
mysql> SELECT NOT NULL;
        -> NULL
mysql> SELECT ! (1+1);
        -> 0
mysql> SELECT ! 1+1;
        -> 1

The last example produces 1 because the expression evaluates the same way as (!1)+1.

AND, &&

Logical AND. Evaluates to 1 if all operands are nonzero and not NULL, to 0 if one or more operands are 0, otherwise NULL is returned.

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

OR, ||

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

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

XOR

Logical XOR. Returns NULL if either operand is NULL. For non-NULL operands, evaluates to 1 if an odd number of operands is nonzero, otherwise 0 is returned.

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

a XOR b is mathematically equal to (a AND (NOT b)) OR ((NOT a) and b).

:=

Assignment operator. Causes the user variable on the left hand side of the operator to take on the value to its right. The value on the right hand side may be a literal value, another variable storing a value, or any legal expression that yields a scalar value, including the result of a query (provided that this value is a scalar value). You can perform multiple assignments in the same SET statement. You can perform multiple assignments in the same statement-

Unlike =, the := operator is never interpreted as a comparison operator. This means you can use := in any valid SQL statement (not just in SET statements) to assign a value to a variable.

mysql> SELECT @var1, @var2;
        -> NULL, NULL
mysql> SELECT @var1 := 1, @var2;
        -> 1, NULL
mysql> SELECT @var1, @var2;
        -> 1, NULL
mysql> SELECT @var1, @var2 := @var1;
        -> 1, 1
mysql> SELECT @var1, @var2;
        -> 1, 1

mysql> SELECT @var1:=COUNT(*) FROM t1;
        -> 4
mysql> SELECT @var1;
        -> 4

You can make value assignments using := in other statements besides SELECT, such as UPDATE, as shown here:

mysql> SELECT @var1;
        -> 4
mysql> SELECT * FROM t1;
        -> 1, 3, 5, 7

mysql> UPDATE t1 SET c1 = 2 WHERE c1 = @var1:= 1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT @var1;
        -> 1
mysql> SELECT * FROM t1;
        -> 2, 3, 5, 7

While it is also possible both to set and to read the value of the same variable in a single SQL statement using the := operator, this is not recommended. Section 9.4, “User-Defined Variables”, explains why you should avoid doing this.

=

This operator is used to perform value assignments in two cases, described in the next two paragraphs.

Within a SET statement, = is treated as an assignment operator that causes the user variable on the left hand side of the operator to take on the value to its right. (In other words, when used in a SET statement, = is treated identically to :=.) The value on the right hand side may be a literal value, another variable storing a value, or any legal expression that yields a scalar value, including the result of a query (provided that this value is a scalar value). You can perform multiple assignments in the same SET statement.

In the SET clause of an UPDATE statement, = also acts as an assignment operator; in this case, however, it causes the column named on the left hand side of the operator to assume the value given to the right, provided any WHERE conditions that are part of the UPDATE are met. You can make multiple assignments in the same SET clause of an UPDATE statement.

In any other context, = is treated as a comparison operator.

mysql> SELECT @var1, @var2;
        -> NULL, NULL
mysql> SELECT @var1 := 1, @var2;
        -> 1, NULL
mysql> SELECT @var1, @var2;
        -> 1, NULL
mysql> SELECT @var1, @var2 := @var1;
        -> 1, 1
mysql> SELECT @var1, @var2;
        -> 1, 1

For more information, see Section 13.7.4, “SET Syntax”, Section 13.2.11, “UPDATE Syntax”, and Section 13.2.10, “Subquery Syntax”.

expr LIKE pat [ESCAPE 'escape_char']

Pattern matching using SQL simple regular expression comparison. Returns 1 (TRUE) or 0 (FALSE). If either expr or pat is NULL, the result is NULL.

The pattern need not be a literal string. For example, it can be specified as a string expression or table column.

Per the SQL standard, LIKE performs matching on a per-character basis, thus it can produce results different from the = comparison operator:

mysql> SELECT 'ä' LIKE 'ae' COLLATE latin1_german2_ci;
+-----------------------------------------+
| 'ä' LIKE 'ae' COLLATE latin1_german2_ci |
+-----------------------------------------+
|                                       0 |
+-----------------------------------------+
mysql> SELECT 'ä' = 'ae' COLLATE latin1_german2_ci;
+--------------------------------------+
| 'ä' = 'ae' COLLATE latin1_german2_ci |
+--------------------------------------+
|                                    1 |
+--------------------------------------+

In particular, trailing spaces are significant, which is not true for CHAR or VARCHAR comparisons performed with the = operator:

mysql> SELECT 'a' = 'a ', 'a' LIKE 'a ';
+------------+---------------+
| 'a' = 'a ' | 'a' LIKE 'a ' |
+------------+---------------+
|          1 |             0 |
+------------+---------------+
1 row in set (0.00 sec)

With LIKE you can use the following two wildcard characters in the pattern.

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

To test for literal instances of a wildcard character, precede it by the escape character. If you do not specify the ESCAPE character, “\” is assumed.

mysql> SELECT 'David!' LIKE 'David\_';
        -> 0
mysql> SELECT 'David_' LIKE 'David\_';
        -> 1

To specify a different escape character, use the ESCAPE clause:

mysql> SELECT 'David_' LIKE 'David|_' ESCAPE '|';
        -> 1

The escape sequence should be empty or one character long. The expression must evaluate as a constant at execution time. If the NO_BACKSLASH_ESCAPES SQL mode is enabled, the sequence cannot be empty.

The following two statements illustrate that string comparisons are not case sensitive unless one of the operands is a binary string:

mysql> SELECT 'abc' LIKE 'ABC';
        -> 1
mysql> SELECT 'abc' LIKE BINARY 'ABC';
        -> 0

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

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

mysql> SELECT filename FROM t1;
+--------------+
| filename     |
+--------------+
| C:           | 
| C:\          | 
| C:\Programs  | 
| C:\Programs\ | 
+--------------+

mysql> SELECT filename, filename LIKE '%\\' FROM t1;
+--------------+---------------------+
| filename     | filename LIKE '%\\' |
+--------------+---------------------+
| C:           |                   0 | 
| C:\          |                   1 | 
| C:\Programs  |                   0 | 
| C:\Programs\ |                   1 | 
+--------------+---------------------+

mysql> SELECT filename, filename LIKE '%\\\\' FROM t1;
+--------------+-----------------------+
| filename     | filename LIKE '%\\\\' |
+--------------+-----------------------+
| C:           |                     0 | 
| C:\          |                     1 | 
| C:\Programs  |                     0 | 
| C:\Programs\ |                     1 | 
+--------------+-----------------------+

expr NOT LIKE pat [ESCAPE 'escape_char']

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

CREATE TABLE foo (bar VARCHAR(10));

INSERT INTO foo VALUES (NULL), (NULL);

SELECT COUNT(*) FROM foo WHERE bar NOT LIKE '%baz%' OR bar IS NULL;

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

STRCMP() performs the comparison using the collation of the arguments.

mysql> SET @s1 = _latin1 'x' COLLATE latin1_general_ci;
mysql> SET @s2 = _latin1 'X' COLLATE latin1_general_ci;
mysql> SET @s3 = _latin1 'x' COLLATE latin1_general_cs;
mysql> SET @s4 = _latin1 'X' COLLATE latin1_general_cs;
mysql> SELECT STRCMP(@s1, @s2), STRCMP(@s3, @s4);
+------------------+------------------+
| STRCMP(@s1, @s2) | STRCMP(@s3, @s4) |
+------------------+------------------+
|                0 |                1 |
+------------------+------------------+

If the collations are incompatible, one of the arguments must be converted to be compatible with the other. See Section 10.1.7.5, “Collation of Expressions”.

mysql> SELECT STRCMP(@s1, @s3);
ERROR 1267 (HY000): Illegal mix of collations (latin1_general_ci,IMPLICIT) and (latin1_general_cs,IMPLICIT) for operation 'strcmp'
mysql> SELECT STRCMP(@s1, @s3 COLLATE latin1_general_ci);
+--------------------------------------------+
| STRCMP(@s1, @s3 COLLATE latin1_general_ci) |
+--------------------------------------------+
|                                          0 |
+--------------------------------------------+

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 which is discussed later in this section. Returns 1 if expr matches pat; otherwise it returns 0. If either expr or pat is NULL, the result is NULL. RLIKE is a synonym for REGEXP, provided for mSQL compatibility.

The pattern need not be a literal string. For example, it can be specified as a string expression or table column.

REGEXP is not case sensitive, except when used with binary strings.

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 character set and collations of the arguments when deciding the type of a character and performing the comparison. If the arguments have different character sets or collations, coercibility rules apply as described in Section 10.1.7.5, “Collation of Expressions”.

^

Match the beginning of a string.

mysql> SELECT 'fo\nfo' REGEXP '^fo$';                   -> 0
mysql> SELECT 'fofo' REGEXP '^fo';                      -> 1

$

Match the end of a string.

mysql> SELECT 'fo\no' REGEXP '^fo\no$';                 -> 1
mysql> SELECT 'fo\no' REGEXP '^fo$';                    -> 0

.

Match any character (including carriage return and newline).

mysql> SELECT 'fofo' REGEXP '^f.*$';                    -> 1
mysql> SELECT 'fo\r\nfo' REGEXP '^f.*$';                -> 1

a*

Match any sequence of zero or more a characters.

mysql> SELECT 'Ban' REGEXP '^Ba*n';                     -> 1
mysql> SELECT 'Baaan' REGEXP '^Ba*n';                   -> 1
mysql> SELECT 'Bn' REGEXP '^Ba*n';                      -> 1

a+

Match any sequence of one or more a characters.

mysql> SELECT 'Ban' REGEXP '^Ba+n';                     -> 1
mysql> SELECT 'Bn' REGEXP '^Ba+n';                      -> 0

a?

Match either zero or one a character.

mysql> SELECT 'Bn' REGEXP '^Ba?n';                      -> 1
mysql> SELECT 'Ban' REGEXP '^Ba?n';                     -> 1
mysql> SELECT 'Baan' REGEXP '^Ba?n';                    -> 0

de|abc

Match either of the sequences de or abc.

mysql> SELECT 'pi' REGEXP 'pi|apa';                     -> 1
mysql> SELECT 'axe' REGEXP 'pi|apa';                    -> 0
mysql> SELECT 'apa' REGEXP 'pi|apa';                    -> 1
mysql> SELECT 'apa' REGEXP '^(pi|apa)$';                -> 1
mysql> SELECT 'pi' REGEXP '^(pi|apa)$';                 -> 1
mysql> SELECT 'pix' REGEXP '^(pi|apa)$';                -> 0

(abc)*

Match zero or more instances of the sequence abc.

mysql> SELECT 'pi' REGEXP '^(pi)*$';                    -> 1
mysql> SELECT 'pip' REGEXP '^(pi)*$';                   -> 0
mysql> SELECT 'pipi' REGEXP '^(pi)*$';                  -> 1

{1}, {2,3}

{n} or {m,n} notation provides a more general way of writing regular expressions that match many occurrences of the previous atom (or “piece”) of the pattern. m and n are integers.

To be more precise, a{n} matches exactly n instances of a. a{n,} matches n or more instances of a. a{m,n} matches m through n instances of a, inclusive.

m and n must be in the range from 0 to RE_DUP_MAX (default 255), inclusive. If both m and n are given, m must be less than or equal to n.

mysql> SELECT 'abcde' REGEXP 'a[bcd]{2}e';              -> 0
mysql> SELECT 'abcde' REGEXP 'a[bcd]{3}e';              -> 1
mysql> SELECT 'abcde' REGEXP 'a[bcd]{1,10}e';           -> 1

[a-dX], [^a-dX]

Matches any character that is (or is not, if ^ is used) either a, b, c, d or X. A - character between two other characters forms a range that matches all characters from the first character to the second. For example, [0-9] matches any decimal digit. To include a literal ] character, it must immediately follow the opening bracket [. To include a literal - character, it must be written first or last. Any character that does not have a defined special meaning inside a [] pair matches only itself.

mysql> SELECT 'aXbc' REGEXP '[a-dXYZ]';                 -> 1
mysql> SELECT 'aXbc' REGEXP '^[a-dXYZ]$';               -> 0
mysql> SELECT 'aXbc' REGEXP '^[a-dXYZ]+$';              -> 1
mysql> SELECT 'aXbc' REGEXP '^[^a-dXYZ]+$';             -> 0
mysql> SELECT 'gheis' REGEXP '^[^a-dXYZ]+$';            -> 1
mysql> SELECT 'gheisa' REGEXP '^[^a-dXYZ]+$';           -> 0

[.characters.]

Within a bracket expression (written using [ and ]), matches the sequence of characters of that collating element. characters is either a single character or a character name like newline. The following table lists the permissible character names.

The following table shows the permissible character names and the characters that they match. For characters given as numeric values, the values are represented in octal.

mysql> SELECT '~' REGEXP '[[.~.]]';                     -> 1
mysql> SELECT '~' REGEXP '[[.tilde.]]';                 -> 1

[=character_class=]

Within a bracket expression (written using [ and ]), [=character_class=] represents an equivalence class. It matches all characters with the same collation value, including itself. For example, if o and (+) are the members of an equivalence class, [[=o=]], [[=(+)=]], and [o(+)] are all synonymous. An equivalence class may not be used as an endpoint of a range.

[:character_class:]

Within a bracket expression (written using [ and ]), [:character_class:] represents a character class that matches all characters belonging to that class. The following table lists the standard class names. These names stand for the character classes defined in the ctype(3) manual page. A particular locale may provide other class names. A character class may not be used as an endpoint of a range.

mysql> SELECT 'justalnums' REGEXP '[[:alnum:]]+';       -> 1
mysql> SELECT '!!' REGEXP '[[:alnum:]]+';               -> 0

[[:<:]], [[:>:]]

These markers stand for word boundaries. They match the beginning and end of words, respectively. A word is a sequence of word characters that is not preceded by or followed by word characters. A word character is an alphanumeric character in the alnum class or an underscore (_).

mysql> SELECT 'a word a' REGEXP '[[:<:]]word[[:>:]]';   -> 1
mysql> SELECT 'a xword a' REGEXP '[[:<:]]word[[:>:]]';  -> 0

In the case of -, +, and *, the result is calculated with BIGINT (64-bit) precision if both operands are integers.

If both operands are integers and any of them are unsigned, the result is an unsigned integer. For subtraction, if the NO_UNSIGNED_SUBTRACTION SQL mode is enabled, the result is signed even if any operand is unsigned.

If any of the operands of a +, -, /, *, % is a real or string value, the precision of the result is the precision of the operand with the maximum precision.

In division performed with /, the scale of the result when using two exact-value operands is the scale of the first operand plus the value of the div_precision_increment system variable (which is 4 by default). For example, the result of the expression 5.05 / 0.014 has a scale of six decimal places (360.714286).

+

Addition:

mysql> SELECT 3+5;
        -> 8

-

Subtraction:

mysql> SELECT 3-5;
        -> -2

-

Unary minus. This operator changes the sign of the operand.

mysql> SELECT - 2;
        -> -2

*

Multiplication:

mysql> SELECT 3*5;
        -> 15
mysql> SELECT 18014398509481984*18014398509481984.0;
        -> 324518553658426726783156020576256.0
mysql> SELECT 18014398509481984*18014398509481984;
        -> out-of-range error

The last expression produces an error because the result of the integer multiplication exceeds the 64-bit range of BIGINT calculations. (See Section 11.2, “Numeric Types”.)

/

Division:

mysql> SELECT 3/5;
        -> 0.60

Division by zero produces a NULL result:

mysql> SELECT 102/(1-1);
        -> NULL

A division is calculated with BIGINT arithmetic only if performed in a context where its result is converted to an integer.

DIV

Integer division. Similar to FLOOR(), but is safe with BIGINT values.

As of MySQL 5.5.3, if either operand has a noninteger type, the operands are converted to DECIMAL and divided using DECIMAL arithmetic before converting the result to BIGINT. If the result exceeds BIGINT range, an error occurs. Before MySQL 5.5.3, incorrect results may occur for noninteger operands that exceed BIGINT range.

mysql> SELECT 5 DIV 2;
        -> 2

N % M, N MOD M

Modulo operation. Returns the remainder of N divided by M. For more information, see the description for the MOD() function in Section 12.6.2, “Mathematical Functions”.

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
mysql> SELECT ACOS(1.0001);
        -> NULL
mysql> SELECT ACOS(0);
        -> 1.5707963267949

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);
        -> 0.20135792079033
mysql> SELECT ASIN('foo');

+-------------+
| ASIN('foo') |
+-------------+
|           0 |
+-------------+
1 row in set, 1 warning (0.00 sec)

mysql> SHOW WARNINGS;
+---------+------+-----------------------------------------+
| Level   | Code | Message                                 |
+---------+------+-----------------------------------------+
| Warning | 1292 | Truncated incorrect DOUBLE value: 'foo' |
+---------+------+-----------------------------------------+

ATAN(X)

Returns the arc tangent of X, that is, the value whose tangent is X.

mysql> SELECT ATAN(2);
        -> 1.1071487177941
mysql> SELECT ATAN(-2);
        -> -1.1071487177941

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);
        -> -0.78539816339745
mysql> SELECT ATAN2(PI(),0);
        -> 1.5707963267949

CEIL(X)

CEIL() is a synonym for CEILING().

CEILING(X)

Returns the smallest integer value not less than X.

mysql> SELECT CEILING(1.23);
        -> 2
mysql> SELECT CEILING(-1.23);
        -> -1

For exact-value numeric arguments, the return value has an exact-value numeric type. For string or floating-point arguments, the return value has a floating-point type.

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'

COS(X)

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

mysql> SELECT COS(PI());
        -> -1

COT(X)

Returns the cotangent of X.

mysql> SELECT COT(12);
        -> -1.5726734063977
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 to be a string and (if possible) is treated as one if it is not.

mysql> SELECT CRC32('MySQL');
        -> 3259397556
mysql> SELECT CRC32('mysql');
        -> 2501908538

DEGREES(X)

Returns the argument X, converted from radians to degrees.

mysql> SELECT DEGREES(PI());
        -> 180
mysql> SELECT DEGREES(PI() / 2);
        -> 90

EXP(X)

Returns the value of e (the base of natural logarithms) raised to the power of X. The inverse of this function is LOG() (using a single argument only) or LN().

mysql> SELECT EXP(2);
        -> 7.3890560989307
mysql> SELECT EXP(-2);
        -> 0.13533528323661
mysql> SELECT EXP(0);
        -> 1

FLOOR(X)

Returns the largest integer value not greater than X.

mysql> SELECT FLOOR(1.23);
        -> 1
mysql> SELECT FLOOR(-1.23);
        -> -2

For exact-value numeric arguments, the return value has an exact-value numeric type. For string or floating-point arguments, the return value has a floating-point type.

FORMAT(X,D)

Formats the number X to a format like '#,###,###.##', rounded to D decimal places, and returns the result as a string. For details, see Section 12.5, “String Functions”.

HEX(N_or_S)

This function can be used to obtain a hexadecimal representation of a decimal number or a string; the manner in which it does so varies according to the argument's type. See this function's description in Section 12.5, “String Functions”, for details.

LN(X)

Returns the natural logarithm of X; that is, the base-e logarithm of X. If X is less than or equal to 0, then NULL is returned.

mysql> SELECT LN(2);
        -> 0.69314718055995
mysql> SELECT LN(-2);
        -> NULL

This function is synonymous with LOG(X). The inverse of this function is the EXP() function.

LOG(X), LOG(B,X)

If called with one parameter, this function returns the natural logarithm of X. If X is less than or equal to 0, then NULL is returned.

The inverse of this function (when called with a single argument) is the EXP() function.

mysql> SELECT LOG(2);
        -> 0.69314718055995
mysql> SELECT LOG(-2);
        -> NULL

If called with two parameters, this function returns the logarithm of X to the base B. If X is less than or equal to 0, or if B is less than or equal to 1, then NULL is returned.

mysql> SELECT LOG(2,65536);
        -> 16
mysql> SELECT LOG(10,100);
        -> 2
mysql> SELECT LOG(1,100);
        -> NULL

LOG(B,X) is equivalent to LOG(X) / LOG(B).

LOG2(X)

Returns the base-2 logarithm of X.

mysql> SELECT LOG2(65536);
        -> 16
mysql> SELECT LOG2(-100);
        -> NULL

LOG2() is useful for finding out how many bits a number requires for storage. This function is equivalent to the expression LOG(X) / LOG(2).

LOG10(X)

Returns the base-10 logarithm of X.

mysql> SELECT LOG10(2);
        -> 0.30102999566398
mysql> SELECT LOG10(100);
        -> 2
mysql> SELECT LOG10(-100);
        -> NULL

LOG10(X) is equivalent to LOG(10,X).

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.

MOD() also works on values that have a fractional part and returns the exact remainder after division:

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

MOD(N,0) returns NULL.

PI()

Returns the value of π (pi). The default number of decimal places displayed is seven, but MySQL uses the full double-precision value internally.

mysql> SELECT PI();
        -> 3.141593
mysql> SELECT PI()+0.000000000000000000;
        -> 3.141592653589793116

POW(X,Y)

Returns the value of X raised to the power of Y.

mysql> SELECT POW(2,2);
        -> 4
mysql> SELECT POW(2,-2);
        -> 0.25

POWER(X,Y)

This is a synonym for POW().

RADIANS(X)

Returns the argument X, converted from degrees to radians. (Note that π radians equals 180 degrees.)

mysql> SELECT RADIANS(90);
        -> 1.5707963267949

RAND(), RAND(N)

Returns a random floating-point value v in the range 0 <= v < 1.0. If a constant integer argument N is specified, it is used as the seed value, which produces a repeatable sequence of column values. In the following example, note that the sequences of values produced by RAND(3) is the same both places where it occurs.

mysql> CREATE TABLE t (i INT);
Query OK, 0 rows affected (0.42 sec)

mysql> INSERT INTO t VALUES(1),(2),(3);
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> SELECT i, RAND() FROM t;
+------+------------------+
| i    | RAND()           |
+------+------------------+
|    1 | 0.61914388706828 |
|    2 | 0.93845168309142 |
|    3 | 0.83482678498591 |
+------+------------------+
3 rows in set (0.00 sec)

mysql> SELECT i, RAND(3) FROM t;
+------+------------------+
| i    | RAND(3)          |
+------+------------------+
|    1 | 0.90576975597606 |
|    2 | 0.37307905813035 |
|    3 | 0.14808605345719 |
+------+------------------+
3 rows in set (0.00 sec)

mysql> SELECT i, RAND() FROM t;
+------+------------------+
| i    | RAND()           |
+------+------------------+
|    1 | 0.35877890638893 |
|    2 | 0.28941420772058 |
|    3 | 0.37073435016976 |
+------+------------------+
3 rows in set (0.00 sec)

mysql> SELECT i, RAND(3) FROM t;
+------+------------------+
| i    | RAND(3)          |
+------+------------------+
|    1 | 0.90576975597606 |
|    2 | 0.37307905813035 |
|    3 | 0.14808605345719 |
+------+------------------+
3 rows in set (0.01 sec)

With a constant initializer, the seed is initialized once when the statement is compiled, prior to execution. If a nonconstant initializer (such as a column name) is used as the argument, the seed is initialized with the value for each invocation of RAND(). (One implication of this is that for equal argument values, RAND() will return the same value each time.)

To obtain a random integer R in the range i <= R < j, use the expression FLOOR(i + RAND() * (j − i)). For example, to obtain a random integer in the range the range 7 <= R < 12, you could use the following statement:

SELECT FLOOR(7 + (RAND() * 5));

RAND() in a WHERE clause is re-evaluated every time the WHERE is executed.

You cannot use a column with RAND() values in an ORDER BY clause, because ORDER BY would evaluate the column multiple times. However, you can retrieve rows in random order like this:

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

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

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