求教一个sql 查询

[zlb789]

表 A
a b c
1 sf t1
2 s t1
3 dd t2
4 dd t3
6 dd t6


现在想一次查询出,每个c类的前2条 , 就是2个t1 ,2个t2 ,.这样的记录 ,c的类别不确定
如果类别确定可以用union 但是类别不确定 如果写?

[CutBug]

declare @A table(a int,  b varchar(2), c nchar(2))
insert into @A
select 1  ,'sf','t1' union all 
select 2  ,'s','t1' union all 
select 3  ,'dd','t2' union all 
select 4  ,'dd','t3' union all 
select 6  ,'dd','t6' union all 
select 7  ,'dd','t2' union all 
select 8  ,'cc','t1' union all 
select 9  ,'a','t2' union all 
select 10  ,'s','t2' 

select * from @A m where a in
  (select top 2 a from @A where c=m.c)
order by m.c 
a           b    c
----------- ---- ----
1           sf   t1
2           s    t1
3           dd   t2
7           dd   t2
4           dd   t3
6           dd   t6

(6 行受影响)

[nj_1st_excellence]

create table tb
(
a int,
b nvarchar(50),
c nvarchar(50),
)
insert tb select 1,'sf','t1'
insert tb select 2,'s','t1'
insert tb select 3,'dd','t2' 
insert tb select 4,'dd','t3'
insert tb select 6,'dd','t6'


select * from tb t where a in
  (select top 2 a from tb where c=t.c)

drop table tb



(1 個資料列受到影響)

(1 個資料列受到影響)

(1 個資料列受到影響)

(1 個資料列受到影響)

(1 個資料列受到影響)
a           b                                                  c
----------- -------------------------------------------------- --------------------------------------------------
1           sf                                                 t1
2           s                                                  t1
3           dd                                                 t2
4           dd                                                 t3
6           dd                                                 t6

(5 個資料列受到影響)

[zlb789]

谢谢
结帖给分

[zzxap]

select top 4 * from @A where c in
(select top 2 c from @A group by c)

[CutBug]

declare @A table(a int,  b varchar(2), c nchar(2))
insert into @A
select 1  ,'sf','t1' union all 
select 2  ,'s','t1' union all 
select 3  ,'dd','t2' union all 
select 4  ,'dd','t3' union all 
select 6  ,'dd','t6' union all 
select 7  ,'dd','t2' 

select top 4 * from @A where c in
(select top 2 c from @A group by c)

a           b    c
----------- ---- ----
1           sf   t1
2           s    t1
3           dd   t2
7           dd   t2

(4 行受影响)

[wuyq11]

在存储过程里通过
insert into #ls select distinct(c) from A
对#ls使用游标也可