常见查询语句：
select .... from .... where .. group by ... having ... order by .. limit...
输出 获取数据 过滤 分组 过滤 排序 限定个数
以上为书写顺序，以下为执行顺序：
from -> where -> group by - >select - > having -> order by -> limit
原文：https://www.cnblogs.com/fjwjw/p/11507294.html