带和/或的where子句中的SQL执行顺序

Question

Does the SQL query

SELECT * FROM table_a where cond1 or cond2 and cond3;

deliver the same result as

SELECT * FROM table_a where (cond1 or cond2) and cond3;

?

Answer 1

No. Boolean operators have precedence rules -- in all programming languages that use them and in mathematics before that. "AND" binds more closely than "OR". This is analogous to arithmetic operators.

Just as:

1 + 2 * 3

is different from:

(1 + 2) * 3

Your two versions are different. AND binds more tightly (like * ). OR less tightly (like + ).