樹的層次體現的sql方案

樹的層次體現的sql方案[@more@]

SQL> select * from test;

ID PARENT_ID
---------- ----------
1 0
2 1
3 2
11 0
22 11
33 22
4 2
44 22

8 rows selected

要得到如下的結果：
ID PARENT_ID 層次
---------- ---------- ----
1 0 0
2 1 1
3 2 2
4 2 2
11 0 0
22 11 1
33 22 2
44 22 2
怎麼寫這個sql？

SELECT ID,PARENT_ID,(LEVEL - 1) AS N
FROM TEST
START WITH PARENT_ID = 0
CONNECT BY PRIOR ID = PARENT_ID;