Question

我有两张表如下

 Table Person

  Id   Name
  1    A
  2    B
  3    C
  4    D
  5    E

Table RelationHierarchy

ParentId   CHildId
    2         1
    3         2
    4         3

这将形成类似树的结构

我正在使用以下CTE来查找顶级父级

  DECLARE @childID INT 
  SET @childID  = 1 --chield to search

  ;WITH RCTE AS
  (
    SELECT *, 1 AS Lvl FROM RelationHierarchy 
    WHERE ChildID = @childID

    UNION ALL

    SELECT rh.*, Lvl+1 AS Lvl FROM dbo.RelationHierarchy rh
    INNER JOIN RCTE rc ON rh.CHildId = rc.ParentId
    )
   SELECT TOP 1 id, Name
   FROM RCTE r
   inner JOIN dbo.Person p ON p.id = r.ParentId
   ORDER BY lvl DESC

现在的问题是，如果人自己是一个顶级的，那么他的身份证应该被退回而不是没有记录。我是否需要临时表或表变量来检查CTE的计数然后返回 @childID如果Count为零？

Answer 1

我认为这可以解决您的问题。这个想法是强迫孩子开始而不是最初进行查找：

WITH RCTE AS
  (
    SELECT @childID as parentId, NULL as childid, 1 AS Lvl

    UNION ALL

    SELECT rh.*, Lvl+1 AS Lvl FROM dbo.RelationHierarchy rh
    INNER JOIN RCTE rc ON rh.CHildId = rc.ParentId
    )
   SELECT TOP 1 id, Name
   FROM RCTE r
   inner JOIN dbo.Person p ON p.id = r.ParentId
   ORDER BY lvl DESC;

查找顶级父级和递归CTE

1 个答案: