mjhjmtu

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