select * from table1 as a where not exists(select 1 from table1 where 班级=a.班级 and 成绩>a.成绩)

------解决方案--------------------
或

SQL code
select * from table1 as a where a.成绩=(select MAX(成绩) from table1 where 班级=a.班级)

------解决方案--------------------
SQL code
use Tempdb
go
--> --> 
 
if not object_id(N'Tempdb..#T') is null
    drop table #T
Go
Create table #T([学号] int,[成绩] int,[班级] nvarchar(3),[考试日期] nvarchar(6))
Insert #T
select 1,100,N'会计2',N'12月1日' union all
select 2,80,N'会计2',N'12月2日' union all
select 3,70,N'会计1',N'12月30日' union all
select 1,90,N'会计2',N'12月1日' union all
select 1,85,N'会计2',N'11月8日' union all
select 2,100,N'会计2',N'12月2日' union all
select 3,80,N'会计1',N'9月30日' union all
select 3,90,N'会计1',N'10月8日'
Go


select * from #T as a where not exists(select 1 from #T where 班级=a.班级 and 成绩>a.成绩)

/*
学号    成绩    班级    考试日期
1    100    会计2    12月1日
2    100    会计2    12月2日
3    90    会计1    10月8日*/

------解决方案--------------------

SQL code
--处理表重复记录(查询和删除)
/******************************************************************************************************************************************************
1、Num、Name相同的重复值记录,没有大小关系只保留一条
2、Name相同,ID有大小关系时,保留大或小其中一个记录
整理人：中国风(Roy)

日期:2008.06.06
******************************************************************************************************************************************************/

--1、用于查询重复处理记录(如果列没有大小关系时2000用生成自增列和临时表处理,SQL2005用row_number函数处理)

--> --> (Roy)生成測試數據
 
if not object_id('Tempdb..#T') is null
    drop table #T
Go
Create table #T([ID] int,[Name] nvarchar(1),[Memo] nvarchar(2))
Insert #T
select 1,N'A',N'A1' union all
select 2,N'A',N'A2' union all
select 3,N'A',N'A3' union all
select 4,N'B',N'B1' union all
select 5,N'B',N'B2'
Go


--I、Name相同ID最小的记录(推荐用1,2,3),方法3在SQl05时，效率高于1、2
方法1:
Select * from #T a where not exists(select 1 from #T where Name=a.Name and ID<a.ID)

方法2:
select a.* from #T a join (select min(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID

方法3:
select * from #T a where ID=(select min(ID) from #T where Name=a.Name)

方法4:
select a.* from #T a join #T b on a.Name=b.Name and a.ID>=b.ID group by a.ID,a.Name,a.Memo having count(1)=1 

方法5:
select * from #T a group by ID,Name,Memo having ID=(select min(ID)from #T where Name=a.Name)

方法6:
select * from #T a where (select count(1) from #T where Name=a.Name and ID<a.ID)=0

方法7:
select * from #T a where ID=(select top 1 ID from #T where Name=a.name order by ID)

方法8:
select * from #T a where ID!>all(select ID from #T where Name=a.Name)

方法9(注:ID为唯一时可用):
select * from #T a where ID in(select min(ID) from #T group by Name)

--SQL2005:

方法10:
select ID,Name,Memo from (select *,min(ID)over(partition by Name) as MinID from #T a)T where ID=MinID

方法11:

select ID,Name,Memo from (select *,row_number()over(partition by Name order by ID) as MinID from #T a)T where MinID=1

生成结果:
/*
ID          Name Memo
----------- ---- ----
1           A    A1
4           B    B1

(2 行受影响)
*/


--II、Name相同ID最大的记录,与min相反:
方法1:
Select * from #T a where not exists(select 1 from #T where Name=a.Name and ID>a.ID)

方法2:
select a.* from #T a join (select max(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID order by ID

方法3:
select * from #T a where ID=(select max(ID) from #T where Name