select *
from tb t
where exists (
    select 1 from tb e where e.class = t.class
    where exists (select 1 from tb where class = e.class 
                      and charindex(','+ltrim(score)+',',','+@ss+',')>0)
    group by class
    having count(distinct score) = len(replace(@ss,',',''))
)

--try !!!

------解决方案--------------------

SQL code
if object_id('[tb]') is not null drop table [tb]
go
create table [tb]([class] varchar(3),[score] int,[checkdate] datetime)
insert [tb]
select '1班','5','2012-1-2' union all
select '2班','4','2012-1-3' union all
select '3班','9','2012-1-6' union all
select '1班','6','2012-1-9' union all
select '2班','6','2012-1-10' union all
select '3班','5','2012-1-11'
go

declare @ss varchar(100)
select @ss = '5,6'
select *
from tb a
join 
  (select class 
   from tb 
   where charindex(','+ltrim(score)+',',','+@ss+',')>0 
   group by class 
   having count(distinct score)=2
) b
on a.class=b.class

/**
class score       checkdate               class
----- ----------- ----------------------- -----
1班    5           2012-01-02 00:00:00.000 1班
1班    6           2012-01-09 00:00:00.000 1班

(2 行受影响)
**/

------解决方案--------------------
SQL code

use [tempdb]
go

if object_id('[tb]') is not null drop table [tb]
go
create table [tb]([class] varchar(3),[score] int,[checkdate] datetime)
insert [tb]
select '1班','5','2012-1-2' union all
select '2班','4','2012-1-3' union all
select '3班','9','2012-1-6' union all
select '1班','6','2012-1-9' union all
select '2班','6','2012-1-10' union all
select '3班','5','2012-1-11'
go

declare @ss varchar(100)
select @ss = '5,6'

;WITH c1 AS
(
SELECT
  CASE WHEN CHARINDEX(CAST(score as varchar(10)), @ss)<>0 THEN 1 ELSE 0 END 'Statistic',
  class,
  score,
  checkdate 
FROM tb
)
, c2 AS
(
SELECT  SUM(Statistic) as 'Combination',class
FROM c1
GROUP BY class )
SELECT tb.*
FROM c2
join tb ON c2.class=tb.class
WHERE c2.Combination=2
--- 试试
--借用下树哥 数据, 嘿嘿……