1．子查詢概念
(1)就是在查詢的where子句中的判斷依據是另一個查詢的結果，如此就構成了一個外部的查詢和一個內部的查詢，這個內部的查詢就是自查詢。
(2)自查詢的分類
1)獨立子查詢
->獨立單值(標量)子查詢(=)

復制代碼 代碼如下:

Select
testID,stuID,testBase,testBeyond,testPro
from Score
where stuID=(
select stuID from Student where stuName='Kencery'
)

復制代碼 代碼如下:

Select
testID,stuID,testBase,testBeyond,testPro
from Score
where stuID in(
select stuID from Student where stuName='Kencery'
)

復制代碼 代碼如下:

use Test
go
create table testNum1
(
Num1 int
);
create table testNum2
(
Num2 int
);
insert into testNum1 values(1),(2),(3)
insert into testNum2 values(4),(5)

復制代碼 代碼如下:

insert into testNum1 values(4),(5),(6),(7),(8),(9),(0)

復制代碼 代碼如下:

select t1.num1,t2.num2 from testNum1 as t1 cross join testNum2 as t2

復制代碼 代碼如下:

Selects1.stuID,
s1.stuName,
s1.stuSex,
s2.testBase,
s2.testBeyond
from Student as s1
inner join Score as s2
on s1.stuID=s2.stuID
where s1.stuIsDel=0;

復制代碼 代碼如下:

create table tblMain
(
ID int,
name nvarchar(20),
fid int
);
create table tblOther
(
ID int,
name nvarchar(20)
)
insert into tblMain values(1,'張三',1),(2,'李四',2)
insert into tblOther values(1,'C++'),(2,'.net'),(3,'java')
select * from
tblMain as t1
inner join
tblOther as t2
on
t1.fid=t2.id

復制代碼 代碼如下:

select * from
tblMain as t1
right join tblOther as t2
on t1.fid=t2.id