> select * from aaa;
+------------+------+------+
| date       | pid  | a    |
+------------+------+------+
| 2009-09-10 |    7 | 5    |
| 2010-10-10 |    7 | 5    |
| 2010-10-10 |    8 | 5    |
| 2010-10-10 |    9 | 5    |
| 2011-11-10 |    7 | 59   |
+------------+------+------+
5 rows in set (0.00 sec)