前言
可以把WITH AS 的用法看成赋值的用法,以减少SQL语句的冗余。当我们在SQL语句中频繁的利用某一个Select查询语句作为数据源时,我们可以用WITH AS 的用法进行简写增加了SQL的易读性,如果构造了多个子查询,结构会更清晰;更重要的是:“一次分析,多次使用”。
语法
with tempName1 as (select ....),tempName2 as (select ....)select ...from tempName
例子
例子:
//普通使用方法Select * from (select name ,age from stuunion select name,age from techunion…)//wtih as with schoolPeople as (select name ,age from stuunion select name,age from techunion…)select * from schoolPeople