层次查询 - 甲骨文

Question

我有一个表有许多项目的ID，并为每一个项目，我有层次结构如下所示。

我输入我的风险id..How可以得到输入风险ID顶层父。

如果我给25作为输入，我应该得到23 output.how我能做到这一点。

Answer 1

从所需行开始上升到根：

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。