I have two tables:
我有两张桌子:
mysql> select * from orders;
+------+---------------------+------------+---------+
| id | created_at | foreign_id | data |
+------+---------------------+------------+---------+
| 1 | 2010-10-10 10:10:10 | 3 | order 1 |
| 4 | 2010-10-10 00:00:00 | 6 | order 4 |
| 5 | 2010-10-10 00:00:00 | 7 | order 5 |
+------+---------------------+------------+---------+
mysql> select * from activities;
+------+---------------------+------------+------+
| id | created_at | foreign_id | verb |
+------+---------------------+------------+------+
| 1 | 2010-10-10 10:10:10 | 3 | get |
| 2 | 2010-10-10 10:10:15 | 3 | set |
| 3 | 2010-10-10 10:10:20 | 3 | put |
| 4 | 2010-10-10 00:00:00 | 6 | get |
| 5 | 2010-10-11 00:00:00 | 6 | set |
| 6 | 2010-10-12 00:00:00 | 6 | put |
+------+---------------------+------------+------+
mysql> select * 
