select 类型,
       时间
from 表 t
where id in(select top 1 id from 表 where 类型=t.类型 order by 时间 desc)

------解决方案--------------------
SQL code
if object_id('[TB]') is not null drop table [TB]
go
create table [TB] (ID int,类型 nvarchar(2),时间 datetime,其它 sql_variant)
insert into [TB]
select 1,'A','2012-04-23 18:00:00',null union all
select 2,'A','2012-04-24 18:00:00',null union all
select 3,'A','2012-04-25 18:00:00',null union all
select 5,'B','2012-04-23 18:00:00',null union all
select 6,'B','2012-04-24 18:00:00',null union all
select 7,'C','2012-04-25 18:00:00',null union all
select 8,'C','2012-04-23 18:00:00',null

select * from [TB]


select distinct B.ID,B.类型,B.时间
from TB A
cross apply(select top 1 ID,类型,时间 from TB where 类型 = A.类型 order by 时间 desc) B


/*
3    A    2012-04-25 18:00:00.000
6    B    2012-04-24 18:00:00.000
7    C    2012-04-25 18:00:00.000*/

------解决方案--------------------
SQL code
;with TT
as(select ROW_NUMBER() over(PARTITION by 类型 order by 时间 desc )as nn ,* from TB)

select ID,类型,时间 from TT where nn = 1