SQLServer子查询

in谓词子查询

select * from dbo.Worker
where did in
(select dID from DepartMent)

比较运算子查询

select * from Worker
where did >
(select Avg(did) from DepartMent)
--any其中一个成立
select * from Worker
where did >
all(select did from DepartMent where did<4)
--all全部成立
select * from Worker
where did >
all(select did from DepartMent where did<2)

子查询代替表达式

select wName,AVG(Gender.Gid) from Worker inner join dbo.Gender
on Worker.gid = Gender.Gid
group by wName
--等同于
select wName,(select avg(Gid) from Gender where Gender.Gid = Worker.Gid ) from Worker

exists子查询

--存在
select * from Worker
where exists(select * from Gender where 1=2)
select * from Worker
where exists(select * from Gender where 1=1)
--不存在
select * from Worker
where not exists(select * from Gender where 1=2)
select * from Worker
where not exists(select * from Gender where 1=1)