內聯接與外聯接的區別通過例項來說明是最清楚的了，下面先準備好測試環境：
create
database test
go
create
table t1 (deptid
int,uname
char(10))
create
table t2 (deptid
int,memo
char(50))
insert
into t1
values(1,
'john')
insert
into t1
values(2,
'tom')
insert
into t1
values(3,
'michal')
insert
into t2
values(1,
'human resources department')
insert
into t2
values(2,
'general accounting department')
insert
into t2
values(4,
'engineering department')
insert
into t2
values(5,
'sales department')
下面依次執行下列語句：
select *
from t1,t2
where t1.deptid=t2.deptid
select *
from t1
inner
join t2
on t1.deptid=t2.deptid
select *
from t1
left
join t2
on t1.deptid=t2.deptid
select *
from t1
right
join t2
on t1.deptid=t2.deptid
select *
from t1
full
join t2
on t1.deptid=t2.deptid
select *
from t1
cross
join t2
語句1和2結果均為：
deptid
uname
deptid
memo
1john
1human resources department
2tom
2general accounting department
<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
可見內聯接與where子句效果一樣。
語句3（左聯）執行結果為：
deptid
uname
deptid
memo
1john
1human resources department
2tom
2general accounting department
3
michael
null
null
語句4（右聯）執行結果為：
deptid
uname
deptid
memo
1john
1 human resources department
2tom
2general accounting department
null
null
4
engineering department
null
null
5
sales department
語句5（全聯）執行結果為：
deptid
uname
deptid
memo
1john
1 human resources department
2tom
2general accounting department
null
null
4
engineering department
null
null
5
sales department
3
michael
null
null
語句6（交叉聯接，注意該語句是沒有on子句的！）執行結果為：
deptid uname deptid memo
1 john 1 human resources department
1 john 2 general accounting department
1 john 4 engineering department
1 john 5 sales department
2 tom 1 human resources department
2 tom 2 general accounting department
2 tom 4 engineering department
2 tom 5 sales department
3 michael 1 human resources department
3 michael 2 general accounting department
3 michael 4 engineering department
3 michael 5 sales department
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