Recursive sum in tree structure

Question

I have a tree struture in a single table. The table is a tree of categories that can be nested endlessly. Each category has a ProductCount column that tells how many product

Answer 1

Actually this could be a good use of HIERARCHYID in SQL Server..

CREATE TABLE [dbo].[CategoryTree]
(
    [Id] INT,
    [ParentId] INT,
    [Name] VARCHAR(100),
    [ProductCount] INT
)
GO

INSERT [dbo].[CategoryTree]
VALUES
    (1, -1, 'Cars', 0),
    (2, -1, 'Bikes', 1),
    (3, 1, 'Ford', 10),
    (4, 3, 'Mustang', 7),
    (5, 3, 'Focus', 4)
    --,(6, 1, 'BMW', 100)
GO

Query

WITH [cteRN] AS (
    SELECT *,
        ROW_NUMBER() OVER (
            PARTITION BY [ParentId] ORDER BY [ParentId]) AS [ROW_NUMBER]
    FROM  [dbo].[CategoryTree]
),
[cteHierarchy] AS (
    SELECT CAST(
            CAST(hierarchyid::GetRoot() AS VARCHAR(100))
            + CAST([ROW_NUMBER] AS VARCHAR(100))
            + '/' AS HIERARCHYID
        ) AS [Node],
        *
    FROM [cteRN]
    WHERE [ParentId] = -1
    UNION ALL
    SELECT CAST(
            hierarchy.Node.ToString()
            + CAST(RN.[ROW_NUMBER] AS VARCHAR(100)
        ) + '/' AS HIERARCHYID),
        rn.*
    FROM [cteRN] rn
    INNER JOIN [cteHierarchy] hierarchy
        ON rn.[ParentId] = hierarchy.[Id]
)
SELECT x.[Node].ToString() AS [Node],
    x.[Id], x.[ParentId], x.[Name], x.[ProductCount],
    x.[ProductCount] + SUM(ISNULL(child.[ProductCount],0))
        AS [ProductCountIncludingChildren]
FROM [cteHierarchy] x
LEFT JOIN [cteHierarchy] child
    ON child.[Node].IsDescendantOf(x.[Node]) = 1
    AND child.[Node] <> x.[Node]
GROUP BY x.[Node], x.[Id], x.[ParentId], x.[Name], x.[ProductCount]
ORDER BY x.[Id]

Result