Assume following table:
假设如下表:
+----+-----------+
| id | session |
+----+-----------+
| 1 | abcd1234 |
| 2 | abcd1234 |
| 3 | abcd1234 |
| 4 | qwert5678 |
| 5 | qwert5678 |
| 6 | abcd1234 |
| 7 | abcd1234 |
| 8 | qwert5678 |
| 9 | abcd1234 |
| 10 | qwert5678 |
| 11 | qwert5678 |
| 12 | qwert5678 |
+----+-----------+
+----+------
