[Js-MySQL]运算符优先级

Posted 2020-10-26 Js_zero

mysql官方文档提供的运算符优先级如下：

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

 1 INTERVAL
 2 BINARY, COLLATE
 3 !
 4 - (unary minus), ~ (unary bit inversion)
 5 ^
 6 *, /, DIV, %, MOD
 7 -, +
 8 <<, >>
 9 &
10 |
11 = (comparison), <=>, >=, >, <=, <, <>, !=, IS, LIKE, REGEXP, IN
12 BETWEEN, CASE, WHEN, THEN, ELSE
13 NOT
14 AND, &&
15 XOR
16 OR, ||
17 = (assignment), :=

 

The precedence of = depends on whether it is used as a comparison operator (=) or as an assignment operator (=). When used as a comparison operator, it has the same precedence as <=>, >=, >, <=, <, <>, !=, IS, LIKE, REGEXP, and IN. When used as an assignment operator, it has the same precedence as :=. Section 13.7.4.1, “SET Syntax for Variable Assignment”, and Section 9.4, “User-Defined Variables”, explain how MySQL determines which interpretation of = should apply.

For operators that occur at the same precedence level within an expression, evaluation proceeds left to right, with the exception that assignments evaluate right to left.

The meaning of some operators depends on the SQL mode:

• 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.

See Section 5.1.8, “Server SQL Modes”.

The precedence of operators determines the order of evaluation of terms in an expression. To override this order and group terms explicitly, use parentheses. For example:

1 mysql> SELECT 1+2*3;
2         -> 7
3 mysql> SELECT (1+2)*3;
4         -> 9