Question

I have a problem that I’m trying to solve that I think is different from other SQL adjacency list hierarchy problems I’ve researched here. I’m trying to sort the data such that all children are listed before any of their parents. I already have CTE’s that return all the children of a given ParentID and all the parents of a given ChildID, but those don’t fit my current need.

I have two tables:

CREATE TABLE [dbo].[ItemMaster](
[ItemID] [int] IDENTITY(1,1) NOT NULL,
[Name] [nvarchar](50) NOT NULL,

CREATE TABLE [dbo].[References](
[RefID] [int] IDENTITY(1,1) NOT NULL,
[ParentID] [int] NOT NULL,
[ChildID] [int] NOT NULL,

Foreign key relationships exist between ItemMaster.ItemID to References.ParentID and References.ChildID

Here’s some example data from my tables…

ItemID, Name

• 1, A1
• 2, A2
• 3, A3
• 4, P1
• 5, P2
• 6, P3
• 7, P4
• 8, TOP

RefID, ParentID, ChildID

• 1,1,5
• 2,2,5
• 3,2,6
• 4,3,2
• 5,7,3
• 6,8,4
• 7,8,1
• 8,8,2
• 9,8,3
• 10,8,7

The output I want would list each ItemID and Name with the children listed before any parents. Like this…

ItemID, Name

• 4, P1
• 5, P2
• 6, P3
• 1, A1
• 2, A2
• 3, A3
• 7, P4
• 8, Top

Notes:

• Any ItemID can have 0, 1 or > 1 parents.
  • Those that don’t have any parents would be listed at the top of the output.
• I don’t have NULL values for the “top most parents” in the reference table.

I hope I’ve given enough detail and explained myself well enough to get some feedback. Any ideas would be greatly appreciated!

Answer 1

I think the way to achieve this is using a recursive operation and assigning a weight to each node, based on the weight of all its children.

For example any leaf in this tree will have a weight of zero since it doesn’t have any children. Its immediate parent will be 1, and the parent’s parent 2 and so on. Sorting on the weight should return the result set you need. Here is the recursive function I used to test my theory:

CREATE FUNCTION [dbo].[GetItemWeight](@ItemID int)
RETURNS int
BEGIN

DECLARE @Weight int;

SELECT
  @Weight = COUNT(ParentID) 
FROM
  [References]
WHERE
  ChildID = @ItemID;

SELECT
  @Weight = ISNULL(@Weight, 0) + SUM(dbo.GetItemWeight(ChildID))
FROM
  [References]
WHERE
  ParentID = @ItemID;

RETURN ISNULL(@Weight, 0);
END

This returns the result set you posted:

SELECT ItemID, Name FROM ItemMaster ORDER BY dbo.GetItemWeight(ItemID);

Best of luck 🙂