ISNULL，SQL，使用select语句作为第二个参数

Question

I don't know if this is possible in SQL or if I have to write a stored procedure but I'm trying to use the ISNULL function as below so that when the parameter @sku is null I'm using a select statement to bring back all the sku's in the table:

SELECT     GooglePrice.idGooglePrice, GooglePrice.idProduct,  products.sku, products.wholeprice, products.price as CurrentHMMPrice, GooglePrice.bestPrice, GooglePrice.link, GooglePrice.title, GooglePrice.description, GooglePrice.ourPrice as PriceCompHMMPrice, 
                      GooglePrice.searchType, GooglePrice.shippingCost, GooglePrice.cheapestOrder, GooglePrice.timeStamp, 
    'ShippingCostNew' = CASE
        WHEN GooglePrice.shippingCost = -1 THEN 'N/A'
        WHEN GooglePrice.shippingCost = 0 THEN 'Free Shipping'
        WHEN GooglePrice.shippingCost > 0 Then cast(GooglePrice.shippingCost as varchar)
        END
FROM         GooglePrice INNER JOIN
                      products ON GooglePrice.idProduct = products.idProduct
WHERE     (products.supplierCode in (@SupplierCode)) AND ISNULL((products.sku like '%'+@sku+'%'), (products.sku in (select sku from products where products.sku)))

ORDER BY GooglePrice.idGooglePrice

Answer 1

Would be easier with an OR

WHERE
     (products.supplierCode in (@SupplierCode)) 
     AND 
     (products.sku like '%'+@SupplierCode+'%' OR @SupplierCode IS NULL)

This was your intention, no?

     AND 
     products.sku like ISNULL('%'+@SupplierCode+'%',products.sku)

Notes:

• leading wildcards can not be optimised and won't use indexes.
• I assume you don't have a CSV in @SupplierCode for this products.supplierCode in (@SupplierCode)

Answer 2

Don't overcomplicate it.

Make your WHERE clause:

WHERE     
   ((products.supplierCode in (@SupplierCode)
       AND 
   (products.sku like '%'+@SupplierCode+'%'))
OR (@suppliercode IS NULL)

You don't really explain your logic so I'm guessing, but the idea is to put a separate check for the NULL comparison.

Answer 3

SELECT GooglePrice.idGooglePrice, GooglePrice.idProduct,  products.sku, products.wholeprice, products.price as CurrentHMMPrice, GooglePrice.bestPrice, GooglePrice.link, GooglePrice.title, GooglePrice.description, GooglePrice.ourPrice as PriceCompHMMPrice, GooglePrice.searchType, GooglePrice.shippingCost, GooglePrice.cheapestOrder, GooglePrice.timeStamp, 
    'ShippingCostNew' = CASE
        WHEN GooglePrice.shippingCost = -1 THEN 'N/A'
        WHEN GooglePrice.shippingCost = 0 THEN 'Free Shipping'
        WHEN GooglePrice.shippingCost > 0 Then cast(GooglePrice.shippingCost as varchar)
        END
FROM  GooglePrice INNER JOIN
      products ON GooglePrice.idProduct = products.idProduct
WHERE (products.supplierCode in (@SupplierCode)) AND (@SupplierCode is null or products.sku like '%'+@SupplierCode+'%')
ORDER BY GooglePrice.idGooglePrice