mysql 执行顺序

Question

请问一下上面语句的执行顺序是什么> sum是最后一步执行的么？ LEFT JOIN 之后 ON WHERE AND 这三个条件是先判断那个一的?

Answer 1

on后的先判断，where后的写在前面的先判断
编号是执行顺序

(7)     SELECT 
(8)     DISTINCT <select_list>
(1)     FROM <left_table>
(3)     <join_type> JOIN <right_table>
(2)     ON <join_condition>
(4)     WHERE <where_condition>
(5)     GROUP BY <group_by_list>
(6)     HAVING <having_condition>
(9)     ORDER BY <order_by_condition>
(10)    LIMIT <limit_number>