oracle with as區(qū)別和用法？With as 就是將一個子查詢的結(jié)果作為一張臨時表，下面接著寫select語句可以通過別名直接使用語法：針對一個別名with tmp as (select

oracle with as區(qū)別和用法？

With as 就是將一個子查詢的結(jié)果作為一張臨時表，下面接著寫select語句可以通過別名直接使用

語法：

針對一個別名

with tmp as (select * from tb_name)

針對多個別名

with

tmp as (select * from tb_name)，

tmp2 as (select * from tb_name2)，

tmp3 as (select * from tb_name3)，

…

例子：

--相當于建了個e臨時表

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

select * from e

--相當于建了e、d臨時表

with

e as (select * from scott.emp)，

d as (select * from scott.dept)

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