SQL语句底层执行顺序

1. SELECT 语句的完整结构

SQL92语法:

SELECT ...,....,(存在聚合函数)

FROM ...,...,...

WHERE 多表的连接条件 AND 不包含聚合函数的过滤条件

GROUP BY ....,....

HAVING 包含聚合函数的过滤条件

ORDER BY .....,....( ASC / DESC )

LIMIT ...,....

SQL99语法

SELECT ...,....,(存在聚合函数)

FROM ... (LEFT / RIGHT)JOIN .... ON

FROM ... (LEFT / RIGHT)JOIN .... ON 多表的连接条件

WHERE 不包含聚合函数的过滤条件

GROUP BY ....,....

HAVING 包含聚合函数的过滤条件

ORDER BY .....,....( ASC / DESC )

LIMIT ...,....

2. SQL语句的执行顺序

FROM -> ON -> (LEFT/RAGHT JOIN) -> WHERE -> GROUP BY -> HAVING ->

SELECT -> DISTINCT ->

ORDER BY -> LIMIT