-->生成测试数据
 
declare @tb table([id] int,[datetime1] Datetime,[number] int)
Insert @tb
select 1,'2008-1-1',5 union all
select 2,'2008-1-2',5 union all
select 3,'2008-1-3',8 union all
select 4,'2008-1-4',7 union all
select 5,'2008-1-5',7
Select top 2 max([id]),max([datetime1]),[number] 
 from @tb
group by [number] 
order by 2 desc
/*
(5 row(s) affected)
                                    number
----------- ----------------------- -----------
5           2008-01-05 00:00:00.000 7
3           2008-01-03 00:00:00.000 8

(2 row(s) affected)



*/

------解决方案--------------------
SQL code
Select top 2 max([id]) as [id] ,convert(nvarchar(10),max([datetime1]),120) as [datetime1],[number] 
 from @tb
group by [number] 
order by 2 desc 
/*
id          datetime1  number
----------- ---------- -----------
5           2008-01-05 7
3           2008-01-03 8

(2 row(s) affected)

*/

------解决方案--------------------
select top 2 * from 表名 where id in (select max(id) from 表名 group by number) order by [datetime1] desc