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

oracle with as區(qū)別和用法？

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

語法：

針對(duì)一個(gè)別名

with tmp as (select * from tb_name)

針對(duì)多個(gè)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(dāng)于建了個(gè)e臨時(shí)表

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

select * from e

--相當(dāng)于建了e、d臨時(shí)表

with

e as (select * from scott.emp)，

d as (select * from scott.dept)

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