Tabela 1
+----+-------+-----------+
| id | campo | criado_em |
| 1  |   a   |   00:00   |
| 2  |   b   |   01:00   |
| 5  |   c   |   04:00   |
+----+-------+-----------+

Tabela 2
+----+-------+-----------+
| id | campo | criado_em |
| 3  |   a   |   02:00   |
| 4  |   b   |   03:00   |
| 6  |   c   |   05:00   |
+----+-------+-----------+