oracle with as 缺点 oracle with as区别和用法？

2021-03-17

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oracle with as区别和用法？With as 就是将一个子查询的结果作为一张临时表，下面接着写select语句可以通过别名直接使用语法：针对一个别名with tmp as (select

oracle with as区别和用法？

With as 就是将一个子查询的结果作为一张临时表，下面接着写select语句可以通过别名直接使用

语法：

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)，

…

例子：

--相当于建了个e临时表

with e as (select * from scott.emp e where e.empno=7499)

select * from e

--相当于建了e、d临时表

with

e as (select * from scott.emp)，

d as (select * from scott.dept)

select * from e， d where e.deptno = d.deptno