I have a table like this:
我有一张这样的桌子:
| id | date | user_id |
----------------------------------------------------
| 1 | 2008-01-01 | 10 |
| 2 | 2009-03-20 | 15 |
| 3 | 2008-06-11 | 10 |
| 4 | 2009-01-21 | 15 |
| 5 | 2010-01-01 | 10 |
| 6 | 2011-06-01 | 10 |
| 7 | 2012-01-01 | 10 |
| 8 | 2008-05-01 | 15 |
| id |