Gfyuki

Given the following query:

SELECT

  p.ProductName,

  CASE

    WHEN EXISTS(SELECT 1 FROM Product WHERE ProductSuperID = p.ProductSuperID AND HasImage = 1)

    THEN

      1

    ELSE

      0

    END

  AS HasImage,

  (SELECT Sum(StockBalance) FROM Product WHERE ProductSuperID = p.ProductSuperID) AS StockBalance,

  CASE

    WHEN EXISTS(SELECT 1 FROM Product WHERE ProductSuperID = p.ProductSuperID AND Price IS NULL)

    AND EXISTS(SELECT 1 FROM Product WHERE ProductSuperID = p.ProductSuperID AND DiscountPrice IS NULL)

    THEN

      0

    ELSE

      1

    END

    AS HasPrice

FROM ProductSuper p



-- SCHEMA

CREATE TABLE ProductSuper

(

  ProductSuperID int,

  ProductName varchar(255)

)

CREATE TABLE Product

(

  ProdID int,

  ProductSuperID int,

  HasImage bit,

  StockBalance int,

  Price decimal(10,2),

  DiscountPrice decimal(10,2)

)

INSERT INTO ProductSuper

  (ProductSuperID, ProductName)

VALUES

  (1, 'Product 1'),

  (2, 'Product 2')

INSERT INTO Product

  (ProductSuperID, HasImage, StockBalance, Price, DiscountPrice)

VALUES

  (1, 0, 10, 10.00, 9.00),

  (1, 0, 0, 10.00, 9.00),

  (2, 0, 10, 10.00, 9.00),

  (2, 0, 2, 10.00, 9.00),

  (2, 1, 5, 10.00, 9.00)

I want to learn how could I best rewrite it to use either JOIN or CROSS APPLY, if anything to avoid some code duplication. I tried writing a JOIN-based version (and one with APPLY) but I'm getting more than one result for each row in the ProductSuper table, whereas I only want one row.

i.e. expected result:

+-------------+-----+-----+-----+

|  Product 1  |  0  |  10 |  1  |

+-------------+-----+-----+-----+

|  Product 2  |  1  |  17 |  1  |

+-------------+-----+-----+-----+

(I'm aware that for this particular piece of code there is little benefit from rewriting, since the subqueries are fast. But still, this is only an example.)

Thanks.

I'd probably structure this query as below

WITH ProductDetails

     AS (SELECT ProductSuperID,

                HasImage = MAX(CASE WHEN HasImage = 1 THEN 1 ELSE 0 END),

                StockBalance = Sum(StockBalance),

                HasPrice = CASE WHEN COUNT(*) = COUNT(Price) AND COUNT(*) = COUNT(DiscountPrice) THEN 1 ELSE 0 END

         FROM   Product

         GROUP  BY ProductSuperID)

SELECT p.ProductName,

       HasImage = ISNULL(pd.HasImage,0),

       pd.StockBalance,

       HasPrice = ISNULL(pd.HasPrice,0)

FROM   ProductSuper p

       LEFT JOIN ProductDetails pd

         ON p.ProductSuperID= pd.ProductSuperID; 

As CROSS APPLY it could be written like this

SELECT ps.ProductName,

       pd.HasImage,

       pd.StockBalance,

       pd.HasPrice

FROM   ProductSuper ps

       CROSS APPLY (SELECT HasImage = MAX(CASE WHEN HasImage = 1 THEN 1 ELSE 0 END),

                           StockBalance = Sum(StockBalance),

                           HasPrice = CASE WHEN COUNT(*) = COUNT(Price) AND COUNT(*) = COUNT(DiscountPrice) THEN 1 ELSE 0 END

                    FROM   Product p

                    WHERE  p.ProductSuperID= ps.ProductSuperID) pd