Mysql SQL执行顺序

SELECT DISTINCT
< select_list >
FROM
< left_table > < join_type >
JOIN < right_table > ON < join_condition >
WHERE
< where_condition >
GROUP BY
< group_by_list >
HAVING
< having_condition >
ORDER BY
< order_by_condition >
LIMIT < limit_number >

-- 行过滤
1 FROM <left_table>
2 ON <join_condition>
3 <join_type> JOIN <right_table> 第二步和第三步会循环执行
4 WHERE <where_condition第四步会循环执行，多个条件的执行顺序是从左往右的。
5 GROUP BY <group_by_list>
6 HAVING <having_condition
--列过滤
7 SELECT 分组之后才会执行SELECT
8 DISTINCT <select_list>
--排序
9 ORDER BY <order_by_condition>
-- MySQL附加
10 LIMIT <limit_number> 前9步都是SQL92标准语法。limit是MySQL的独有语法。