sql数据分组（GROUP BY）最大值，第一条，前三条实例

SELECT  课程,
        SUM(奖金) AS 奖金
FROM    ( SELECT    课程,
                    学号,
                    成绩
          FROM      考试 AS a
          WHERE     ( SELECT    COUNT(*)
                      FROM      考试
                      WHERE     课程 = a.课程
                                AND 学号 <> a.学号
                                AND 成绩 > a.成绩
                    ) < 3
        ) AS b
GROUP BY 课程

declare @Tab table
(Num int, Name varchar(2),   Time DATETIME)
insert into @tab select 1    ,'a',        '2009/05/01'
insert into @tab select 1    ,'a',        '2009/05/02'
insert into @tab select 1    ,'a',        '2009/05/03'
insert into @tab select 2    ,'b',        '2009/05/04'
insert into @tab select 2    ,'b',        '2009/05/05'
insert into @tab select 3    ,'c',        '2009/05/06'
insert into @tab select 3    ,'c',        '2009/05/07'
insert into @tab select 5    ,'e',        '2009/05/08'
insert into @tab select 1    ,'a',        '2009/05/09'
insert into @tab select 1    ,'a',        '2009/05/10'

select  * from @Tab t where  not exists(select 1 from @Tab where num=t.num and [time]

/*
Num         Name Time
----------- ---- -----------------------
1           a    2009-05-01 00:00:00.000
2           b    2009-05-04 00:00:00.000
3           c    2009-05-06 00:00:00.000
5           e    2009-05-08 00:00:00.000

(4 行受影响)
*/