Question

I found this nice example of SQL recursion with a CTE, but fail to apply it to my table:

• http://walkingoncoals.blogspot.de/2009/12/fun-with-recursive-sql-part-1.html

I have the following table (ObjectStates):

ID    Title    ParentID
1     Draft    null
2     Green    null
3     Red      null
4     Foo      1
5     Bar      4

I am trying to create a function which returns the “main” state when queried. Example:

GetMainState(5)
-- Shall return 1
GetMainState(4)
-- Shall return 1
GetMainState(2)
-- Shall return 2

I have so far:

CREATE FUNCTION [dbo].[GetMainObjectState] (@ObjectStateID INT)
RETURNS TABLE
AS
RETURN 
(
 WITH StateRecurcsion(ID, ParentID, Level) AS
       (
           SELECT ID, ParentID, 0
           FROM ObjectStates
           WHERE ID = @ObjectStateID
           UNION ALL
           SELECT uOS.ID, uOS.ParentID, sOS.Level+1
           FROM ObjectStates uOS, StateRecurcsion sOS
           WHERE uOS.ParentID= sOS.ID
       )
 SELECT os.ID, os.Title, sos.Level
 FROM ObjectStates os, StateRecurcsion sos
 WHERE os.ID = sos.ID
)
GO

I tried to create the function just as in the tutorial shown above, but somehow I’m not getting the correct results.

Answer 1

You could create a CTE containing a “root” value and then query it within your function e.g.:

;WITH CTEHierarchy
AS (
    SELECT 
    ID
        ,0 AS LEVEL
        ,ID AS root

    FROM ObjectStates
    WHERE  ParentID IS NULL

    UNION ALL

    SELECT 
    ObjectStates.ID
        ,LEVEL + 1 AS LEVEL
        ,[root]

    FROM ObjectStates
    INNER JOIN CTEHierarchy uh ON uh.id = ObjectStates.ParentID
    )    
    SELECT [root]
    FROM CTEHierarchy
    WHERE ID = @ObjectStateID