Question

SQL Server两表联合查询问题

表A：
Aid Bid
1 1
2 2
3
4 3
表B
Bid text
1 A
2 B
3 C

需要查询结果如下表：
Aid text
1 A
2 B
3
4 C

Answer 1

declare @tab1 table (id int,value nvarchar(20) null)
declare @tab2 table (id int,value nvarchar(20))

insert into @tab1
select 1,'1'
union
select 2,'2'
union
select 3,null
union
select 4,'3'

insert into @tab2
select 1,'A'
union
select 2,'B'
union
select 3,'C'

update a set a.value=b.value
from @tab1 a
left join @tab2 b
on convert(int,a.value)=b.id
where convert(int,a.value)=b.id

select * from @tab1

Answer 2

select C.CID, A.Aid,B.text from A left join B on A.Aid = B.Bid right join C on C.AID=A.AID

Answer 3

select A.Aid,B.text from A left join B on A.Bid = B.Bid

追问

如果再加一个表C,和表A关联
Cid Aid
1 1
2
3 4
4 3
查询出表C的1 3 4对应的A.Aid和B.text
如何查询呢?