WITH AS短语,也叫做子查询部分(subquery factoring),可以让你做很多事情,定义一个SQL片断,该SQL片断会被整个SQL语句所用到。有的时候,是为了让SQL语句的可读性更高些,也有可能是在UNION ALL的不同部分,作为提供数据的部分。
with as 用法–针对一个别名
with tmp as (select * from tb_name)
–针对多个别名
with
tmp as (select * from tb_name),
tmp2 as (select * from tb_name2),
tmp3 as (select * from tb_name3),
…
–相当于建了个e暂时表
with e as (select * from scott.emp e where e.empno=7499)
select * from e;
–相当于建了e、d暂时表
with
e as (select * from scott.emp),
d as (select * from scott.dept)
select * from e, d where e.deptno = d.deptno;
来源:高三网
能发现自己知识上的薄弱环节,在上课前补上这部分的知识,不使它成为听课时的“绊脚石”。这样,就会顺利理解新知识,相信通过with as 用法这篇文章能帮到你,在和好朋友分享的时候,也欢迎感兴趣小伙伴们一起来探讨。