删除重复记录

Question

表T有3列:
empid int,
checkdate datetime,
chektime  datetime假设有以下数据：1 2009-06-23 00:00:00.000 1900-01-01 18:01:10.000
1 2009-06-23 00:00:00.000 1900-01-01 18:02:30.000
1 2009-06-23 00:00:00.000 1900-01-01 18:02:50.000
2 2009-06-15 00:00:00.000 1900-01-01 08:42:23.000
2 2009-06-16 00:00:00.000 1900-01-01 08:42:41.000
2 2009-06-17 00:00:00.000 1900-01-01 08:46:03.000
2 2009-06-17 00:00:00.000 1900-01-01 18:20:10.000
2 2009-06-15 00:00:00.000 1900-01-01 18:17:08.000
2 2009-06-16 00:00:00.000 1900-01-01 18:10:00.000
同一天同一小时同一分钟的认为是重复数据，如何用一条语句删掉重复的数据？（重复的数据保留一条，任意一条都行）
删除后的数据应该是这样：
1 2009-06-23 00:00:00.000 1900-01-01 18:01:10.0001 2009-06-23 00:00:00.000 1900-01-01 18:02:50.0002 2009-06-16 00:00:00.000 1900-01-01 08:42:41.000
2 2009-06-17 00:00:00.000 1900-01-01 08:46:03.000
2 2009-06-17 00:00:00.000 1900-01-01 18:20:10.000
2 2009-06-15 00:00:00.000 1900-01-01 18:17:08.000
2 2009-06-16 00:00:00.000 1900-01-01 18:10:00.000

Answer 1

delete a from T a where chektime 
 not in(select min(chektime) from T 
         where convert(varchar(16),chektime,120)=convert(varchar(16),chektime,120))

Answer 2

DELETE A 
FROM T A 
WHERE NOT EXISTS(SELECT 1 FROM T B WHERE A.empid=B.empid AND A.chektime>B.chektime)

Answer 3

delete from T a
where exists (select 1 from T where empid=a.empid and checkdate=a.checkdate
and convert(varchar(16),chektime,120)=convert(varchar(16),a.chektime,120)
and chektime>a.chektime
)