我有一个表，其中存储了一个活动列表，其时间间隔由 2 个日期分隔。
样本：
+------+---------------------+---------------------+-------------+
| name | start | end | time (calc) |
+------+---------------------+---------------------+-------------+
| me | 2017-04-03 11:00:00 | 2017-04-03 11:30:00 | 30 |
| me | 2017-04-03 23:45:00 | 2017-04-04 00:15:00 | 30 |
| me | 2017-04-04 10:00:00 | 2017-04-04 11:00:00 | 60 |
| me | 2017-04-04 10:30:00 | 2017-04-04 11:30:00 | 60 |
| me | 2017-04-05 23:00:00 | 2017-04-05 23:30:00 | 30 |
| me | 2017-04-05 23:15:00 | 2017-04-07 00:45:00 | …