Question

I’m trying to query a few tables in our db that contains product data. It is a MSSQL 2005 database. The problem is its returning multiple rows for one product when I need it to only produce one row per product. Blow is the query and results I’m using.

SELECT      ProductItem.sku, ProductItem.title, ProductItem.short_desc, ProductItem.long_desc, ProductItem.active, ProductItem.product_item_id, 
                    ProductCategory.category_desc, ProductCategoryMap.product_id, ProductCategory.active AS activecat, Product.adwords_label, 
                    ProductItem.item_price, ProductItem.sale_price
FROM          Product INNER JOIN
                        ProductCategoryMap INNER JOIN
                        ProductCategory ON ProductCategoryMap.product_category_id = ProductCategory.product_category_id ON 
                        Product.product_id = ProductCategoryMap.product_id FULL OUTER JOIN
                        ProductItem ON Product.product_key = ProductItem.sku
WHERE      (ProductItem.active = 1) AND (ProductCategory.active = 1)

This returns the following results:

I know the problem occurs because the product resides in multiple categories, but really I don’t need every category its in, just one of them. So ideally just one product for every row returned

I can’t figure out how to make my query achieve that though.

Can anyone help me out please?

Answer 1

At first glance, take category columns out and add DISTINCT. You’ve asked for “category” so you can get all categories.

Also:

• the WHERE changes your FULL OUTER JOIN to an INNER
• get product_id from Product
• the activecat column is implied by the where clause anyway

I’ve tweaked it for clarity and added an aggregate to get one category

SELECT
   PI.sku, PI.title, PI.short_desc, PI.long_desc, 
   PI.active, PI.product_item_id, 
   PI.item_price, PI.sale_price, 

   MIN(PC.category_desc),
   P.product_id,
   1 AS activecat, --implied by filter

   P.adwords_label
FROM 
    ProductItem PI
    INNER JOIN
    Product P ON P.product_key = PI.sku
    INNER JOIN
    ProductCategoryMap PCM ON P.product_id = PCM.product_id
    INNER JOIN
    ProductCategory PC ON PCM.product_category_id = PC.product_category_id
WHERE
   (PI.active = 1) AND (PC.active = 1)
GROUP BY
   PI.sku, PI.title, PI.short_desc, PI.long_desc, 
   PI.active, PI.product_item_id, 
   PI.item_price, PI.sale_price, 
   P.product_id,
   P.adwords_label

Edit: you can tidy it more with APPLY which will also deal with no categories if changed to OUTER APPLY

SELECT
   PI.sku, PI.title, PI.short_desc, PI.long_desc, 
   PI.active, PI.product_item_id, 
   PI.item_price, PI.sale_price, 

   PC2.category_desc,
   P.product_id,
   PC2.active AS activecat,

   P.adwords_label
FROM 
    ProductItem PI
    INNER JOIN
    Product P ON P.product_key = PI.sku
    CROSS APPLY
    (
    SELECT TOP 1
        PC.category_desc, PC.active
    FROM
        ProductCategoryMap PCM
        INNER JOIN
        ProductCategory PC ON PCM.product_category_id = PC.product_category_id
    WHERE
       P.product_id = PCM.product_id AND PC.active = 1
    ORDER BY 
       PC.category_desc
    ) PC2
WHERE
   PI.active = 1