with t as (select * from scott.emp where 1=1)
select * from t where empno='';
select * from (
select sal as salary,comm as commission from scott.emp ) x
where salary <5000;
-- 内聯視圖
内聯視圖通常是指 一個SQL查詢的結果作為另一個查詢的資料源, 一般在 From字句後面
select p.pname,c1_sum1,c2_sum2
from p,
(select id,sum(q1) c1_sum1 from s1 group by id) s1,
(select id,sum(q2) c2_sum2 from s2 group by id) s2
where p.id=s1.id
and p.id=s2.id
-- 标量子查詢
select
p.pname,
(select sum(q1) c1_sum1 from s1 where s1.id=p.id) c1_sum1,
(select sum(q2) c1_sum1 from s2 where s2.id=p.id) c2_sum2
from p
-- with子查詢分解
主要是友善了解,增加可讀性
with c1_vw as (select id,sum(q1) sum1 from s1 group by id),
c2_vw as (select id,sum(q2) sum2 from s2 group by id),
c1_c2 as (select t1.id,t1.sum1,t2.sum2 from c1_vw t1,c2_vw t2 where t1.id=t2.id)
select p.pname,sum1,sum2
from p,c1_c2
where p.id=c1_c2.id