Question

I want to return all products from the Product table based on any category in the hierarchy.

For example, you could search products by all “Fords” (category = 1) and it would return two results.

Right now, this recursive result returns the products only if there is an exact match in the product table to the CategoryHierarchy table. So it works if I say category = 4.

In the product table, I have two Ford Mustangs. Only the price and description are different (not shown here), but their classification is the same in terms of the product categories.

[Product Table]
[ProductId] [ProductName] [CategoryId]
1       Ford Mustang 1     4
2       Ford Mustang 2     4
3       Buick Regal 3      12

Each Ford Mustang has the CategoryHierarchy that goes 1,2,3,4. Those same two results should show up if the Sql parameter lowestcategory is 1 OR 2 OR 3 OR 4. Right now, it only works if it = 4.

[CategoryHierarchy]
[Id]    [parentId]  [categoryName]
1       0           Ford
2       1           Mustang
3       2           2010
4       3           Blue
10      0           Buick
11      10          Regal
12      11          1999

MS SQL 2008:

declare @lowestcategoryid int;

set @lowestcategoryid = 4;--returns the products but I need it to work if this var = 1,2,3 too

--recursive loop
with RecursiveResult( id, CategoryName, ProductName, parentId) as
(
select ch.Id, ch.categoryname, p.productname, ch.parentId
from CategoryHierarchy ch 
join product p on p.categoryId = ch.id
where ch.id = @lowestcategoryid

UNION ALL

select p.categoryId, ch.categoryName, p.productname, ch.parentId
from product p
join CategoryHierarchy ch on p.categoryId = ch.id
join RecursiveResult r on ch.parentId = r.Id 

)

select * from recursiveresult

Answer 1

I think you want to separate out the recursive portion (traversing the CategoryHierarchy table) from the join on Product. Start at the lowest (or “highest”) category and move deeper, and finally join that set on Product… like this:

DECLARE @lowestcategoryid INT;

SET @lowestcategoryid = 3;

--recursive loop
WITH RecursiveResult( id, CategoryName, parentId) AS
(
SELECT ch.Id, ch.categoryname, ch.parentId
FROM CategoryHierarchy ch 
WHERE ch.id = @lowestcategoryid

UNION ALL

SELECT ch.Id, ch.categoryname, ch.parentId
FROM CategoryHierarchy ch 
    JOIN RecursiveResult r 
        ON r.Id = ch.ParentId

)

SELECT * 
FROM recursiveresult r
    JOIN Product p
        ON p.CategoryId = r.Id