如何查询出每个人每天中最晚一次记录时间，ORACLE MSSQL均可！
数据库结构为：
用户名 操作时间
MMM 2009-9-5 18:21:56
MMM 2009-9-6 8:35:20
MMM 2009-9-6 8:38:10
LL 2009-9-6 9:29:27
LL 2009-9-6 9:40:40
KKK 2009-9-6 10:09:50
KKK 2009-9-6 11:09:38
MMM 2009-9-6 15:14:25
MMM 2009-9-6 15:18:04
MMM 2009-9-6 18:19:03
MMM 2009-9-6 18:19:14
MMM 2009-9-6 18:19:32
KKK 2009-9-7 8:52:51
KKK 2009-9-7 8:54:14
KKK 2009-9-7 9:28:01
KKK 2009-9-7 9:36:25
KKK 2009-9-7 9:41:54
KKK 2009-9-7 9:42:19
KKK 2009-9-7 9:42:33
KKK 2009-9-7 9:47:50
KKK 2009-9-7 9:48:26
KKK 2009-9-7 9:48:51
KKK 2009-9-7 9:49:19
KKK 2009-9-7 9:49:23
KKK 2009-9-7 9:50:30
KKK 2009-9-7 9:50:35
KKK 2009-9-7 10:08:21
KKK 2009-9-7 10:34:02
KKK 2009-9-7 10:54:57
MMM 2009-9-7 10:55:09
KKK 2009-9-7 11:15:54
KKK 2009-9-7 11:31:04
KKK 2009-9-7 11:31:17
KKK 2009-9-7 11:31:58
KKK 2009-9-7 11:32:25
KKK 2009-9-7 11:34:03
KKK 2009-9-7 11:34:23
LL 2009-9-7 11:42:37
KKK 2009-9-7 11:43:13
KKK 2009-9-7 11:47:14
KKK 2009-9-7 11:49:38
MMM 2009-9-7 11:50:54
MMM 2009-9-7 11:51:45
KKK 2009-9-7 11:51:51
KKK 2009-9-7 11:52:24
LL 2009-9-7 12:07:49
MMM 2009-9-7 14:27:51
KKK 2009-9-7 14:28:40
KKK 2009-9-7 14:29:01
KKK 2009-9-7 14:32:38
LL 2009-9-7 14:38:57
LL 2009-9-7 14:43:50
LL 2009-9-7 14:44:11
KKK 2009-9-7 14:56:03
LL 2009-9-7 14:56:50
KKK 2009-9-7 14:57:14
KKK 2009-9-7 14:57:51
4
KKK 2009-9-7 18:17:28
KKK 2009-9-7 18:22:01
KKK 2009-9-7 18:22:08
KKK 2009-9-7 18:26:06
KKK 2009-9-7 18:26:11
KKK 2009-9-7 18:33:19
KKK 2009-9-7 18:33:35
KKK 2009-9-7 18:37:56
KKK 2009-9-8 7:56:01
KKK 2009-9-8 14:42:01
KKK 2009-9-8 15:14:41
KKK 2009-9-8 15:15:33
KKK 2009-9-8 15:15:37
KKK 2009-9-8 15:18:02
KKK 2009-9-8 15:20:26
KKK 2009-9-8 15:25:42
KKK 2009-9-8 15:26:14
LL 2009-9-8 15:30:13
KKK 2009-9-8 15:30:17
LL 2009-9-8 15:31:44
LL 2009-9-8 15:31:56
LL 2009-9-8 15:38:51
LL 2009-9-8 16:02:25
KKK 2009-9-8 16:33:03
KKK 2009-9-8 17:59:15
KKK 2009-9-8 18:04:30
KKK 2009-9-8 18:20:15
KKK 2009-9-8 19:53:08
Admin 2009-9-8 19:55:58
Admin 2009-9-8 19:59:08
KKK 2009-9-8 19:59:24
KKK 2009-9-9 8:44:14
KKK 2009-9-9 8:44:52