如题：（数据忘记排序了）
[td]

Obs	TRANS_AT	DATE	TIME	time_ll1
1	12000.00	2013-11-16	10:07:49	9:07:49
2	10000.00	2013-11-16	10:11:29	9:11:29
3	12000.00	2013-11-18	10:34:07	9:34:07
4	1760.00	2013-11-18	11:21:33	10:21:33
5	14000.00	2013-11-19	20:32:07	19:32:07
6	23000.00	2013-11-19	20:33:01	19:33:01
7	50000.00	2013-11-21	15:22:16	14:22:16
8	29000.00	2013-11-21	15:23:13	14:23:13
9	4900.00	2013-11-21	15:25:20	14:25:20
10	2445.00	2013-11-21	15:26:18	14:26:18
11	992.00	2013-11-23	13:22:59	12:22:59
12	992.00	2013-11-23	13:23:30	12:23:30
13	820.00	2013-11-29	9:16:48	8:16:48
14	110000.00	2013-11-29	10:56:09	9:56:09
15	50000.00	2013-11-29	10:56:48	9:56:48
16	60000.00	2013-11-29	10:57:35	9:57:35
17	50000.00	2013-11-29	10:58:06	9:58:06
18	10000.00	2013-11-29	10:58:32	9:58:32
19	8170.00	2013-11-29	11:11:44	10:11:44
20	10000.00	2013-11-29	11:12:14	10:12:14
21	3000.00	2013-11-29	11:13:27	10:13:27
22	5000.00	2013-11-29	11:14:45	10:14:45
23	3582.00	2013-11-29	11:15:16	10:15:16
24	50000.00	2013-11-29	11:17:59	10:17:59
25	23070.00	2013-11-29	12:22:14	11:22:14
26	880.00	2013-11-29	12:38:56	11:38:56
27	10115.00	2013-12-19	11:33:23	10:33:23
28	239.00	2013-12-19	14:21:48	13:21:48
29	523.00	2013-12-19	14:25:24	13:25:24
30	268.00	2013-12-19	14:25:49	13:25:49

数据给出了金额、日期、时间、倒退一个小时的时点，
希望对于每一条观测，求当前时点前一个小时的额度累计。
还望大虾们赐教！