DECLARE @ProductID INT = 711
DECLARE @StartDate DATETIME
DECLARE @StandardCost MONEY
SELECT
pch.ProductID
,pch.StartDate
,pch.StandardCost
FROM Production.ProductCostHistory pch
WHERE pch.ProductID = ISNULL(@ProductID, pch.ProductID)
AND pch.StartDate = ISNULL(@StartDate, pch.StartDate)
AND pch.StandardCost = ISNULL(@StandardCost, pch.StandardCost)