如何使用mysql查询订购记录？

Question

我有User表，其中包含以下列id，ancestor_id，parent_id，level。我想根据按级别排序的parent_id列出用户。

select id, name, ancestor_id, parent_id, level from users;
+------+---------+-------------+-----------+-------+
| id   | name    | ancestor_id | parent_id | level |
+------+---------+-------------+-----------+-------+
|    1 | John    |        NULL |         1 |     0 |
|    2 | Mark    |           1 |         1 |     0 |
|    3 | Stephen |           1 |         1 |     1 |
|    4 | Richard |           1 |         2 |     0 |
|    5 | Michael |           1 |         2 |     1 |
|    6 | Paul    |           1 |         2 |     2 |
|    7 | Emily   |           1 |         6 |     0 |
|    8 | Mathew  |           1 |         6 |     1 |
+------+---------+-------------+-----------+-------+

输出：

John
  Mark (first level)
    Richard (2nd level)
    Michael (2nd level)
    Paul    (2nd level)
      Emily (3rd level)
      Mathew (3rd level)
  Stephen(first level)

如何编写mysql以列出按其适当父级的级别排序的用户？