MySQL uses some standard SQL operators and some non-standard operators. They can be used to write expressions which involve constant values, variables, values contained in fields and / or other expressions.
If you want to check if 2 values are equal, you must use the = operator:
SELECT True = True -- returns 1 SELECT True = False -- returns 0
If you want to check if 2 values are different, you can use the <> or != operators, which have the same meaning:
SELECT True <> False -- returns 1 SELECT True != True -- returns 0
<> return 1 where = returns 0 and vice versa.
When you compare a NULL value with a non-NULL value, you'll get NULL. If you want to check if a value is null, you can use IS:
SELECT (NULL IS NULL) -- returns 1 SELECT (1 IS NULL) -- returns 0 SELECT (True IS True) -- returns an error!
You can check if a value is non-NULL:
SELECT (True IS NOT NULL) -- returns 1
There is also an equality operator which considers NULL as a normal value, so it returns 1 (not NULL) if both values are NULL and returns 0 (not NULL) if one of the values is NULL:
SELECT NULL <=> NULL -- 1 SELECT True <=> True -- 1 SELECT col1 <=> col2 FROM myTable
There is not a NULL-safe non-equality operator, but you can type the following:
SELECT NOT (col1 <=> col2) FROM myTable
IS and IS NOT can also be used for Boolean comparisons. You can use them with the reserved words TRUE, FALSE and UNKNOWN (which is merely a synonym for NULL).
SELECT 1 IS TRUE -- returns 1 SELECT 1 IS NOT TRUE -- returns 0 SELECT 1 IS FALSE -- returns 0 SELECT (NULL IS NOT FALSE) -- returns 1: unknown is not false SELECT (NULL IS UNKOWN) -- returns 1 SELECT (NULL IS NOT UNKNOWN) -- returns 0
You can check if a value is greater than another value:
SELECT 100 > 0 -- returns 1 SELECT 4 > 5 -- return 0
You can also check if a value is minor than another value:
SELECT 1 < 2 -- returns 1 SELECT 2 < 2 -- returns 0
This kind of comparisons also works on TEXT values:
SELECT 'a' < 'b' -- returns 1
Generally speaking, alphabetical order is used for TEXT comparisons. However, the exact rules are defined by the COLLATION used. A COLLATION defines the sorting rules for a given CHARACTER SET. For example, a COLLATION may be case-sensitive, while another COLLATION may be case-insensitive.
You can check if a value is equal or greater than another value. For example, the following queries have the same meaning:
SELECT `a` >= `b` FROM `myTable` SELECT NOT (`a` < `b`) FROM `myTable`
Similarly, you can check if a value is less or equal to another value:
SELECT `a` <= `b` FROM `myTable`
If you want to check if a value is included in a given range (boundaries included), you can use the BETWEEN ... AND ... operator. AND doesn't have its usual meaning. Example:
SELECT 2 BETWEEN 10 AND 100 -- 0 SELECT 10 BETWEEN 10 AND 100 -- 1 SELECT 20 BETWEEN 10 AND 100 -- 1
The value after BETWEEN and the value after AND are included in the range.
You can also use NOT BETWEEN to check if a value is not included in a range:
SELECT 8 NOT BETWEEN 5 AND 10 -- returns 0
You can use the IN operator to check if a value is included in a list of values:
SELECT 5 IN (5, 6, 7) -- returns 1 SELECT 1 IN (5, 6, 7) -- returns 0
You should not include in the list both numbers and strings, or the results may be unpredictable. If you have numbers, you should quote them:
SELECT 4 IN ('a', 'z', '5')
There is not a theoretical limit to the number of values included in the IN operator.
You can also use NOT IN:
SELECT 1 NOT IN (1, 2, 3) -- returns 0
MySQL doesn't have a real BOOLEAN datatype.
FALSE is a synonym for 0. Empty strings are considered as FALSE in a Boolean context.
TRUE is a synonym for 1. All non-NULL and non-FALSE data are considered as TRUE in a boolean context.
UNKNOWN is a synonym for NULL. The special date 0/0/0 is NULL.
NOT is the only operator which has only one operand. It returns 0 if the operand is TRUE, returns 1 if the operand is FALSE and returns NULL if the operand is NULL.
SELECT NOT 1 -- returns 0 SELECT NOT FALSE -- returns 1 SELECT NOT NULL -- returns NULL SELECT NOT UNKNOWN -- returns NULL
! is a synonym for NOT.
AND returns 1 if both the operands are TRUE, else returns 0; if at least one of the operands is NULL, returns NULL.
SELECT 1 AND 1 -- returns 1 SELECT 1 AND '' -- return 0 SELECT '' AND NULL -- returns NULL
&& is a synonym for AND.
SELECT 1 && 1
OR returns TRUE if at least one of the operands is TRUE, else returns FALSE; if the two operands are NULL, returns NULL.
SELECT TRUE OR FALSE -- returns 1 SELECT 1 OR 1 -- returns 1 SELECT FALSE OR FALSE -- returns 0 SELECT NULL OR TRUE -- returns NULL
|| is a synonym for OR.
SELECT 1 || 0
XOR (eXclusive OR) returns 1 if only one of the operands is TRUE and the other operand is FALSE; returns 0 if both the operands are TRUE o both the operands are FALSE; returns NULL if one of the operands is NULL.
SELECT 1 XOR 0 -- returns 1 SELECT FALSE XOR TRUE -- returns 1 SELECT 1 XOR TRUE -- returns 0 SELECT 0 XOR FALSE -- returns 0 SELECT NULL XOR 1 -- returns NULL
Only NOT (usually) has a different precedence from its synonym. See operator precedence for detail.
MySQL supports operands which perform all basic arithmetic operations.
You can type positive values with a '+', if you want:
SELECT +1 -- return 1
You can type negative values with a '-'. - is an inversion operand:
SELECT -1 -- returns -1 SELECT -+1 -- returns -1 SELECT --1 -- returns 1
You can make sums with '+':
SELECT 1 + 1 -- returns 2
You can make subtractions with '-':
SELECT True - 1 -- returns 0
You can multiply a number with '*':
SELECT 1 * 1 -- returns 1
You can make divisions with '/'. Returns a FLOAT number:
SELECT 10 / 2 -- returns 5.0000 SELECT 1 / 1 -- returns 1.0000 SELECT 1 / 0 -- returns NULL (not an error)
You can make integer divisions with DIV. Resulting number is an INTEGER. No reminder. This has been added in MySQL 4.1.
SELECT 10 DIV 3 -- returns 3
You can get the reminder of a division with '%' or MOD:
SELECT 10 MOD 3 -- returns 1
You can convert an INTEGER to a FLOAT doing so:
SELECT 1 + 0.0 -- returns 1.0 SELECT 1 + 0.000 -- returns 1.000 SELECT TRUE + 0.000 -- returns 1.000
You can't convert a string to a FLOAT value by adding 0.0, but you can cast it to an INTEGER:
SELECT '1' + 0 -- returns 1 SELECT '1' + FALSE -- returns 1 SELECT <nowiki>''</nowiki> + <nowiki>''</nowiki> -- returns 0
There are no concatenation operators in MySQL.
Arithmetic operators convert the values into numbers and then perform arithmetic operations, so you can't use + to concatenate strings.
You can use the CONCAT function instead.
The LIKE operator may be used to check if a string matches to a pattern. A simple example:
SELECT * FROM articles WHERE title LIKE 'hello world'
The pattern matching is usually case insensitive. There are two exceptions:
SELECT * 'test' LIKE BINARY 'TEST' -- returns 0
You can use two special characters for LIKE comparisons:
Note that "\" also escapes quotes ("'") and this behaviour can't be changed by the ESCAPE clause. Also, the escape character does not escape itself.
Common uses of LIKE:
SELECT * FROM articles WHERE title LIKE 'hello%'
SELECT * FROM articles WHERE title LIKE '%world'
SELECT * FROM articles WHERE title LIKE '%gnu%'
These special chars may be contained in the pattern itself: for example, you could need to search for the "_" character. In that case, you need to "escape" the char:
SELECT * FROM articles WHERE title LIKE '\_%' -- titles starting with _ SELECT * FROM articles WHERE title LIKE '\%%' -- titles starting with %
Sometimes, you may want to use an escape character different from "\". For example, you could use "/":
SELECT * FROM articles WHERE title LIKE '/_%' ESCAPE '/'
When you use = operator, trailing spaces are ignored. When you use LIKE, they are taken into account.
SELECT 'word' = 'word ' -- returns 1 SELECT 'word' LIKE 'word ' -- returns 0
LIKE also works with numbers.
SELECT 123 LIKE '%2%' -- returns 1
If you want to check if a pattern doesn't match, you can use NOT LIKE:
SELECT 'a' NOT LIKE 'b' -- returns 1
You can use SOUNDS LIKE to check if 2 text values are pronounced in the same way. SOUNDS LIKE uses the SOUNDEX algorithm, which is based on English rules and is very approximate (but simple and thus fast).
SELECT `word1` SOUNDS LIKE `word2` FROM `wordList` -- short form SELECT SOUNDEX(`word1`) = SOUNDEX(`word2`) FROM `wordList` -- long form
SOUNDS LIKE is a MySQL-specific extension to SQL. It has been added in MySQL 4.1.
You can use REGEXP to check if a string matches to a pattern using regular expressions.
SELECT 'string' REGEXP 'pattern'
You can use RLIKE as a synonym for REGEXP.
SELECT ~0 -- returns 18446744073709551615 SELECT ~1 -- returns 18446744073709551614
SELECT 1 & 1 -- returns 1 SELECT 1 & 3 -- returns 1 SELECT 2 & 3 -- returns 2
SELECT 1 | 0 -- returns 1 SELECT 3 | 0 -- returns 3 SELECT 4 | 2 -- returns 6
SELECT 1 ^ 0 -- returns 1 SELECT 1 ^ 1 -- returns 0 SELECT 3 ^ 1 -- returns 2
SELECT 1 << 2 -- returns 4
SELECT 1 >> 2 -- 0
IF ... THEN ... ELSE ... END IF; only functions in the stored procedures. To manage a condition out of them, we can use:
IF(condition, ifTrue, ifFalse);.
SELECT IF(-1 < 0, 0, 1); returns 0.
IF n > m THEN SET s = '>'; ELSEIF n = m THEN SET s = '='; ELSE SET s = '<'; END IF;
SELECT CASE WHEN condition THEN ifTrue ELSE ifFalse END;
SELECT CASE WHEN '-1 < 0' THEN 0 ELSE 1 END; renvoie 0.
Example with several conditions:
CASE v WHEN 2 THEN SELECT v; WHEN 3 THEN SELECT 0; ELSE BEGIN END; END CASE;
In one request:
SELECT CASE v WHEN 1 THEN 'a' WHEN 2 THEN 'b' WHEN 3 THEN 'c' WHEN 4 THEN 'd' ELSE 0 END as value
Table of operator precedence:
INTERVAL BINARY, COLLATE ! - (unary minus), ~ (unary bit inversion) ^ *, /, DIV, %, MOD -, + <<, >> & | =, <=>, >=, >, <=, <, <>, !=, IS, LIKE, REGEXP, IN BETWEEN, CASE, WHEN, THEN, ELSE NOT &&, AND XOR ||, OR :=
You can use parenthesis to force MySQL to evaluate a subexpression before another independently from operator precedence:
SELECT (1 + 1) * 5 -- returns 10
You can also use parenthesis to make an expression more readable by humans, even if they don't affect the precedence:
SELECT 1 + (2 * 5) -- the same as 1 + 2 * 5
You can use the = operator to assign a value to a column:
UPDATE `myTable` SET `uselessField`=0
When you want to assign a value to a variable, you must use the := operator, because the use of = would be ambiguous (is it as assignment or a comparison?)
SELECT @myvar := 1
You can also use SELECT INTO to assign values to one or more variables.
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