+------------+-------------+-------------+-------------+
| date | riverbasin1 | riverbasin2 | riverbasin3 |
+------------+-------------+-------------+-------------+
| 2014122500 | undefined | undefined | undefined |
| 2015121300 | 0 | 0 | 0 |
| 2015121400 | 1 | 0 | 0 |
| 2015121500 | 0 | 0 | 0 |
| 2015121600 | 0 | 0 | 0 |
| 2015121700 | 0 | 0 | 0 |
| 2015121800 | 0 | 1 | 0 |
| 2015121900 | undefined | undefined | undefined |
| 2015122000 | 0 | 0 | 0 |
| 2015122100 | 0 | 5 | 6 |
| 2015122200 | 0 | 0 | 0 |
| 2015122300 | 0 | 0 | 0 |
| 2015122300 | 0 | 0 | 1 |
| 2015122400 | 0 | 1 | 1 |
| 2015122400 | 0 | 2 | 1 |
| 2015122400 | 0 | 2 | 0 |
| 2015122500 | undefined | undefined | undefined |
| 2015122600 | 0 | 0 | 0 |
| 2015122700 | 1 | 1 | 0 |
| 2015122900 | undefined | undefined | undefined |
+------------+-------------+-------------+-------------+
MySQL表中有一些重复日期，如2014122400和2015122300及其riverbasin值中的相应记录
我想只保留与上次重复日期对应的最后一条记录，并删除其他重复日期及其值。