Oracle：递归自引用连接第 n 级记录

Question

我有这样的自我参考table：

id   |level | parent_id
----------------------
1    |1     |null
2    |1     |null
3    |2     |1
4    |2     |1
5    |2     |2
6    |3     |5
7    |3     |3
8    |4     |7
9    |4     |6
------------------------

我需要第 n 级家长作为结果。例如二级家长

id   |level | parent_id| second_level_parent_id
------------------------------------------------
1    |1     |null      |null
2    |1     |null      |null
3    |2     |1         |null
4    |2     |1         |null
5    |2     |2         |null
6    |3     |5         |5
7    |3     |3         |3
8    |4     |7         |3
9    |4     |6         |5
-------------------------------------------------

Answer 1

这对我有用。

SELECT m.*,
  CONNECT_BY_ROOT id AS second_level_parent_id
FROM my_table m
WHERE CONNECT_BY_ROOT level =2
  CONNECT BY prior id    = parent_id;

感谢@Jozef Dúc