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

select distinct 
       a.ChildID,a.ParentID,
       --isnull(nullif(c.parentID,b.parentID),a.parentID) as toppa,
       B.parentID
       --,c.parentID
      ,isnull(nullif(d.parentID,a.parentID),c.parentID) as toppa1,a.name
from myTable a
   inner join myTable c
       on a.parentID=c.parentID
   inner join myTable b
       on b.childID=a.parentID
   inner join myTable d
       on d.childID=b.parentID  

I have using the without CTE expression and then using joins to get the step to step parent for child and then more important Common table expressions were introduced in SQL Server 2005 not in server 2000 so using joins to get values this is basic way for to get parentid for a child value

Answer 2

select dbo.[fn_getIMCatPath](8)
select Cat_id,Cat_name,dbo.[fn_getIMCatPath](cat_id) from im_category_master

Create FUNCTION [dbo].[fn_getIMCatPath] (@ID INT) 
returns NVARCHAR(1000) 
AS 
BEGIN 
  DECLARE @Return   NVARCHAR(1000), 
          @parentID INT, 
          @iCount   INT 

  SET @iCount = 0 

  SELECT @Return = Cat_name, 
         @parentID = parent_id 
  FROM   im_category_master 
  WHERE  [cat_id] = @ID 

  WHILE @parentID IS NOT NULL 
    BEGIN 
        SELECT @Return = cat_name + '>' + @Return, 
               @parentID = parent_id 
        FROM   im_category_master 
        WHERE  [cat_id] = @parentID 

        SET @iCount = @iCount + 1 
        IF @parentID = -1
        BEGIN
        SET @parentID = NULL 
        END
        IF @iCount > 10 
          BEGIN 
              SET @parentID = NULL 
              SET @Return = '' 
          END 
    END 

  RETURN @Return 
END

Answer 3

Consider this sample data and respective SQL to access child records along with their top parent.

Sample DATA

SQL code:

;WITH c AS (
   SELECT Id, Name, ParentId as CategoryId, 
          Id as MainCategoryId, Name AS MainCategory 
     FROM   pmsItemCategory 
     WHERE  ParentId is null

     UNION ALL 

     SELECT T.Id, T.Name, T.ParentId,  MainCategoryId, MainCategory 
     FROM   pmsItemCategory AS T 
            INNER JOIN c  ON T.ParentId = c.Id 
     WHERE  T.ParentId is not null
    ) 

SELECT Id, Name, CategoryId, MainCategoryId, MainCategory 
FROM   c 
order by Id

Answer 4

With cte as 
(
Select ChileId,Name,ParentId from tblHerarchy
where ParentId is null 
union ALL
Select h.ChileId,h.Name,h.ParentId  from cte
inner join tblHerarchy h on h.ParentId=cte.ChileId
) 
Select * from cte

Answer 5

select distinct 
       a.ChildID,a.ParentID,
       --isnull(nullif(c.parentID,b.parentID),a.parentID) as toppa,
       B.parentID
       --,c.parentID
      ,isnull(nullif(d.parentID,a.parentID),c.parentID) as toppa1,a.name
from myTable a
   inner join myTable c
       on a.parentID=c.parentID
   inner join myTable b
       on b.childID=a.parentID
   inner join myTable d
       on d.childID=b.parentID

Answer 6

Not sure I understand what you are looking for but it could be this.

;WITH c 
     AS (SELECT childid, 
                parentid, 
                parentid AS topParentID 
         FROM   @myTable 
         WHERE  childid = parentid 
         UNION ALL 
         SELECT T.childid, 
                T.parentid, 
                c.topparentid 
         FROM   @myTable AS T 
                INNER JOIN c 
                        ON T.parentid = c.childid 
         WHERE  T.childid <> T.parentid) 
SELECT childid, 
       topparentid 
FROM   c 
ORDER  BY childid 

SE-Data

It is the same as answer by marc_s with the difference that I use your table variable and the fact that you have childID = parentID for root nodes where the answer by marc_s has parent_ID = null for root nodes. In my opinion it is better to have parent_ID = null for root nodes.