mysql学习03-sql执行加载顺序

Posted 2021-03-04 classBug

1.sql语句

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_conddition>

limit <limit_num>

 

2.mysql服务器处理后的顺序

from left_table

on join_condition

join_type join right_table

where where_condition

group by group_by_list

having having_condition

select

distinct select_list

order by order_by_condition

limit limit_num

顺序：先确定要查询的表，

然后where条件过滤数据，

group by进行分组，

having条件过滤每个组中的数据，

确定要查询的字段，

对于查出来信息进行排序

限制查询数据的量。