这里有一张像
这样的表格DATE | Duration
2013-11-30 00:00:00 | 2000000
2013-11-30 00:01:00 | 3000000
2013-11-30 00:02:00 | 2000000
2013-11-30 00:04:00 | 4000000
2013-11-30 00:23:00 | 2000000
2013-11-30 00:45:00 | 7000000
2013-11-30 01:00:00 | 5000000
2013-11-30 01:02:00 | 4000000
2013-11-30 01:03:00 | 12000000
2013-11-30 01:05:00 | 52000000
2013-11-30 01:07:00 | 2000000
2013-11-30 01:12:00 | 13000000
2013-11-30 02:02:00 | 5000000
2013-11-30 02:04:00 | 21000000
2013-11-30 02:07:00 | 33000000
2013-11-30 02:08:00 | 2000000
2013-11-30 02:12:00 | 9000000
2013-11-30 02:24:00 | 18000000
2013-11-30 02:26:00 | 7000000
2013-11-30 02:29:00 | 8000000
如何获得每小时的中位数？
例如，结果应为：
NTH_HOUR | MIDDLE_DURATION
1 | 3000000
2 | 13000000
3 | 8000000
谢谢！