求一个SQL查询语句

[annywoody]

表rt_value有三个字段id，value，time
id value time
1 0.12 2009-05-31 08:30:15
2 0.14 2009-05-31 08:21:15
1 0.52 2009-05-31 08:02:15
3 0.32 2009-05-31 08:45:15
2 0.72 2009-05-31 08:15:15
3 0.18 2009-05-31 08:23:15
2 0.52 2009-05-31 08:46:15

现在要搜索每个id的最新的value，sql语句怎么写？？

我现在是获取每个id然后再循环查询的，效率很低了
select top 1 id,value,time
from rt_value
order by time desc
能否有一个语句就查出所有结果呢？？

[yanjing_mail]

select * from rt_value t where not exists(select 1 from rt_value where id=t.id and time>t.time)

[yanjing_mail]

or

select * from rt_value as a where time = (select MAX(time) from dd where id = a.id)

[biweilun]

select * from rt_value as a where time = (select MAX(time) from a where id = a.id)

[annywoody]

ok
谢谢ls的了
回去好好研究下sql语句的具体含义