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