求去重复值SQL

[felix3118]

现有数据
c2 c1 uid uid2
3 4 2 1
NULL 3 3 1
3 4 1 2
2 3 3 2
NULL 3 1 3
2 3 2 3

如何写SQL语句实现过滤UID,UID2相同的数据
最后结果为：

c2 c1 uid uid2
3 4 1 2
NULL 3 1 3
2 3 2 3

[dawugui]

select m.* from tb m, tb n where m.uid = n.uid2 and m.uid2 = n.uid and m.uid < n.uid2

[dawugui]

create table tb(c2 int,c1 int,uid int,uid2 int)
insert into tb values(3    ,4 ,2 ,1)
insert into tb values(NULL ,3 ,3 ,1)
insert into tb values(3    ,4 ,1 ,2)
insert into tb values(2    ,3 ,3 ,2)
insert into tb values(NULL ,3 ,1 ,3)
insert into tb values(2    ,3 ,2 ,3)

go

select m.* from tb m, tb n where m.uid = n.uid2 and m.uid2 = n.uid and m.uid < m.uid2

drop table tb

/*
c2          c1          uid         uid2        
----------- ----------- ----------- ----------- 
3           4           1           2
NULL        3           1           3
2           3           2           3

（所影响的行数为 3 行）
*/

[「已注销」]

怎么过滤的？没看懂。

[水族杰纶]

if not object_id('tb') is null
	drop table tb
Go
Create table tb([c2] int,[c1] int,[uid] int,[uid2] int)
Insert tb
select 3,4,2,1 union all
select null,3,3,1 union all
select 3,4,1,2 union all
select 2,3,3,2 union all
select null,3,1,3 union all
select 2,3,2,3
Go
select c2,
       c1,
       min([Uid])[Uid],
       max([Uid])[Uid2]
from(
Select [c2],[c1],[Uid]  from tb
union 
Select [c2],[c1],[Uid2]  from tb
)t
group by c2,c1
/*
c2          c1          Uid         Uid2
----------- ----------- ----------- -----------
NULL        3           1           3
2           3           2           3
3           4           1           2
*/