求SELECT语句：保留一字段的最大的那行
直接上表结构：
表名：ESD_VOL_MONITOR
列：
EQPID varchar(50)： 可能会有很多重复的
ESD_VOL float： 浮点型数字
MONITOR_TIME datetime： 时间
表的内容举例说明如下

EQPID ESD_VOL MONITOR_TIME
1SASY07-P1 40 2013-02-21 18:54:29
1SASY07-P2 30 2013-02-22 18:54:29
1SASY07-P1 20 2013-02-23 18:54:29
1SASY07-P3 10 2013-02-24 18:54:29
1SASY07-P1 50 2013-02-25 18:54:29
1SASY07-P6 20 2013-02-26 18:54:29
1SASY07-P2 40 2013-02-27 18:54:29
1SASY07-P5 40 2013-02-28 18:54:29
1SASY07-P3 40 2013-02-29 18:54:29

我要得到的结果是：
相同EQPID且MONITOR_TIME是最大的，上面的话应该返回
1SASY07-P1 50 2013-02-25 18:54:29
1SASY07-P2 40 2013-02-27 18:54:29
1SASY07-P3 40 2013-02-29 18:54:29


请指点
[解决办法]
select * from ESD_VOL_MONITOR a where exists
(select 1 from ESD_VOL_MONITOR where a.EQPID=EQPID
group by EQPID having max(MONITOR_TIME)=a.MONITOR_TIME)
[解决办法]

select * from ESD_VOL_MONITOR  t where MONITOR_TIME=(select max(MONITOR_TIME) from ESD_VOL_MONITOR  where EQPID=t.EQPID)

[解决办法]

select ESD_VOL,EQPID,MONITOR_TIME from ESD_VOL_MONITOR a inner join
(select EQPID,max(MONITOR_TIME ) id from ESD_VOL_MONITOR group by EQPID) b
on a.EQPID=b.EQPID and a.MONITOR_TIME =b.MONITOR_TIME
[解决办法]

select ESD_VOL,EQPID,MONITOR_TIME from ESD_VOL_MONITOR a inner join 
(select EQPID,max(MONITOR_TIME ) id from ESD_VOL_MONITOR group by EQPID) b
on a.EQPID=b.EQPID and a.MONITOR_TIME =b.MONITOR_TIME

[解决办法]
一楼的答案很正确，又学了点东西啊