withas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;