求一个简单的SQL语句!

[shangnong_1999]

表中字段dm有重复的数据,数据例子如下:
dm mc
0000 a
0000 ab
0001 b
0001 bc
求一个SQL语句实现以下结果:
dm mc
0000 a
0001 b

[vivianfdlpw]

select * from 表 t
where mc=(select min(mc) from 表 where dm=t.dm)

[vivianfdlpw]

declare @tb table
(
dm varchar(10),
mc varchar(10)
)
insert @tb
select '0000','a' union
select '0000','ab' union
select '0001','b' union
select '0001','bc'

--查询
select * from @tb t
where mc=(select min(mc) from @tb where dm=t.dm)

--结果
/*
dm mc
---------- ----------
0000 a
0001 b

（所影响的行数为 2 行）
*/

[duoluohuifeng]

SELECT select * from 表 t WHERE LEN(mc)=(SELECT MIN(LEN(MC)) FROM 表 WHERE DM=T.DM)

[shangnong_1999]

字段mc是随便的,没有规律

[$扫地僧$]

select dm ,left(mc,1) from 表 group by dm ,left(mc,1)

[yinguangbo]

select distinct t1.dm,t2.mc from tb as t1 left join tb as t2 on t1.dm=t2.dm
你试试这个语句,如果left join 不成,可以试试right join和inner join

[brooks105]

select * from a s
where not exists(select 1 from a
where a.dm=s.dm
and a.mc<s.mc)

[liuyinbo0109]

declare @a table
( dm char(10),
mc char(10)
)
insert @a
select '0000','a'
union all
select '0000','ab'
union all
select '0001','b'
union all
select '0001','bc'

select dm,min(mc) from @a group by dm