我想按时间戳合并两个数据帧。但是时间戳列具有相同的名称，但有点不同，这里是我的数据框：df1：
Timestamp Flag Group
1438 2019-10-25 10:39:58.352073 begin prod
1439 2019-10-25 10:40:06.266782 end prod
1440 2019-10-25 16:35:22.485574 begin clean
1441 2019-10-27 09:50:31.713192 end clean
1442 2019-10-28 14:04:33.095633 begin transport
1443 2019-10-28 14:05:07.639344 end transport
df2:
Timestamp
1438 2019-10-25 10:39:58.352073
1439 2019-10-25 10:40:06.266782
1440 2019-10-25 16:35:22.485574
1441 2019-10-25 17:00:00.000000
1442 2019-10-26 07:00:00.000000
1443 2019-10-26 17:00:00.000000
1444 2019-10-27 07:00:00.000000
1445 2019-10-27 09:50:31.713192
1446 2019-10-28 14:04:33.095633
1447 2019-10-28 14:05:07.639344
结果必须是：
Timestamp Flag Group
1438 2019-10-25 10:39:58.352073 begin prod
1439 2019-10-25 10:40:06.266782 end prod
1440 2019-10-25 16:35:22.485574 begin clean
1441 2019-10-25 17:00:00.000000 NaN NaN
1442 2019-10-26 07:00:00.000000 NaN NaN
1443 2019-10-26 17:00:00.000000 NaN NaN
1444 2019-10-27 07:00:00.000000 NaN NaN
1445 2019-10-27 09:50:31.713192 end clean
1446 2019-10-28 14:04:33.095633 begin transport
1447 2019-10-28 14:05:07.639344 end transport
我尝试使用连接，但是名为时间戳的两列之间存在唯一性问题。所以我不知道如何解决这个问题......