SQL语句的书写顺序和执行顺序

sql语句的书写顺序:

select >> from >> where >> group by >> having >> order by >> limit
注意：
1. select和from是必须的；
2. where和having不能同时使用;
3. having和group by联合使用；

sql语句的解析顺序 :

from >> on>> join >> where >> group by >> having >> select >> distinct >> order by >> limit
注意：虽然select在having后执行，但是mysql中仍然可以在having中使用select语句定义的别名

select [ALL | DISTINCT | DISTINCTROW | TOP] 字段
from 表
[inner join  right join | left join 表2]
[on 连接条件]
[where 条件]
[group by 分组规则]
[having 分组条件]
[order by 排序规则]
[limit 分页规则]