public int UpdateAmountInStock(Product _product, int _amount) { string query = "DECLARE @Difference int SET @Difference = (SELECT AmountInStock FROM Product WHERE ID = @ProductID) + @AmountDelivered IF @Difference < 0 SET @AmountDelivered = @AmountDelivered - @Difference; UPDATE Product SET AmountInStock = AmountInStock + @AmountDelivered WHERE ID = @ProductID SELECT @AmountDelivered AS 'Result'"; List <KeyValuePair <string, object> > parameterlist = new List <KeyValuePair <string, object> > { new KeyValuePair <string, object>("@AmountDelivered", _amount), new KeyValuePair <string, object>("@ProductID", _product.ID) }; return(SQL_CRUD_Methods.SQLUpdateReturnInt(query, parameterlist)); }