Sql 在oracle中查找层次结构中的最后一个子级

我有一张像这样的桌子

prnt_id   child_id
-----------------
1           2
2           4
3
5
6           7
7           8
8           9

我的结果应该包含

prnt_id  child_id
-----------------
1          4
3
5
6          9

我正在使用oracle 10g

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我尝试使用“连接方式”执行此操作，但没有得到预期的结果

使用CONNECT_BY_ROOT从根获取prnt_id，并使用CONNECT_BY_ISLEAF指示叶节点所在的位置。类似的方法应该会奏效：

SELECT PRNT_ID, 
       CHILD_ID
FROM (SELECT CONNECT_BY_ROOT PRNT_ID PRNT_ID, CHILD_ID, CONNECT_BY_ISLEAF leaf 
      FROM TABLE
      CONNECT BY PRIOR CHILD_ID = PRNT_ID
      START WITH prnt_id NOT IN (SELECT CHILD_ID
                                 FROM TABLE
                                 WHERE CHILD_ID IS NOT NULL))
WHERE leaf = 1

例如，这将为您提供所需的结果：

WITH dat AS (SELECT 1 prnt_id, 2 child_id FROM DUAL
             UNION ALL
             SELECT 2 prnt_id, 4 child_id FROM DUAL
             UNION ALL
             SELECT 3 prnt_id, NULL child_id FROM DUAL
             UNION ALL
             SELECT 5 prnt_id, NULL child_id FROM DUAL
             UNION ALL
             SELECT 6 prnt_id, 7 child_id FROM DUAL
             UNION ALL
             SELECT 7 prnt_id, 8 child_id FROM DUAL
             UNION ALL             
             SELECT 8 prnt_id, 9 child_id FROM DUAL)
SELECT PRNT_ID, 
       CHILD_ID
FROM (SELECT CONNECT_BY_ROOT PRNT_ID PRNT_ID, CHILD_ID, CONNECT_BY_ISLEAF leaf FROM dat
      CONNECT BY PRIOR CHILD_ID = PRNT_ID
      START WITH prnt_id NOT IN (SELECT CHILD_ID
                                 FROM dat
                                 WHERE CHILD_ID IS NOT NULL))
WHERE leaf = 1


PRNT_ID CHILD_ID
1       4
3   
5   
6       9

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您当前的代码是什么？你能详细说明你想做什么吗？我正在尝试获取根节点的最后一个节点，而不管它与什么直接或间接相关。谢谢@Mikhail..这成功了。我正在做的是选择CONNECT\U BY\U ROOT PRNT\U ID PRNT\U ID，CHILD\U ID，CONNECT\U BY\U ISLEAF leaf FROM dat CONNECT BY PRNT\U ID=PRNT\U ID从PRNT\U ID开始。