分层查询 - Oracle

Question

我有一个包含许多项目ID的表，对于每个项目，我都有如下的层次结构。

我的输入是风险ID。如何获得输入风险ID的顶级父级。

如果我将25作为输入，我应该得到23作为输出。我可以实现这一点。

Answer 1

从所需的行开始并上升到根目录：

SELECT RiskID,
FROM   PROJECT_RISKS
WHERE  CONNECT_BY_ISLEAF = 1
START WITH
       RiskID    = 25
CONNECT BY
       PRIOR Link2 = Link1
AND    PRIOR ProjectID = ProjectID;

从根开始并下降到所需的行：

SELECT  CONNECT_BY_ROOT( RiskID ) AS RiskID
FROM    Project_Risks
WHERE   RiskID    = 25
START WITH
        link2     IS NULL
CONNECT BY
       PRIOR Link1 = Link2
AND    PRIOR ProjectID = ProjectID;

两者都会给出相同的答案。