SQL Server CTE -Find top parentID forEach childID?

Question

I have a table which contains hierarchy data - something like:

childID  |  parentID
____________________
  1      |     5
  5      |     9
  9      |     20         


        

Answer 1

I have not yet the time to look further into your question and am not sure whether or not i've understood your problem, but couldn't you use this svf to get the top father's id?

CREATE FUNCTION [dbo].[getTopParent] (
    @ChildID INT
)

RETURNS int
AS
BEGIN
    DECLARE @result int;
    DECLARE @ParentID int;

    SET @ParentID=(
        SELECT ParentID FROM ChildParent
        WHERE ChildID = @ChildID 
    )

    IF(@ParentID IS NULL)
        SET @result = @ChildID 
    ELSE
        SET @result = [dbo].[getTopParent](@ParentID)

    RETURN @result    
END

Then you should be able to find each top parent in this way:

SELECT ChildID
    ,  [dbo].[getTopParent](ChildID) AS TopParentID
FROM ChildParent