What is the difference between the actual manufacturing cost of product number 818 and the estimated manufacturing cost?
product number 818 refers to ProductID = 818; estimated manufacturing cost refers PlannedCost; actual manufacturing cost refers to ActualCost; difference = Substract(PlannedCost(ProductID(818))),(ActualCost(ProductID(818)));
SELECT PlannedCost - ActualCost FROM WorkOrderRouting WHERE ProductID = 818