我有一个这样的简单表格:
+------------+---------+-----------+--------------+
| comment_id | post_id | parent_id | comment_text |
+------------+---------+-----------+--------------+
| 1 | 200 | 0 | a |
| 2 | 200 | 0 | b |
| 3 | 200 | 1 | c |
| 4 | 200 | 1 | d |
| 5 | 200 | 0 | e |
| 6 | 200 | 2 | f |
| 7 | 200 | 2 | g |
| 8 | 200 | …