Creating a Trigger in MySQL that stores stock levels once a sale takes place
You must use SUM function with orderPrice

SELECT SUM(ORDERS.OrderPrice), SUPPLIER.SupplierName FROM ((ORDERS INNER JOIN PRODUCT ON ORDERS.ProductID = PRODUCT.ProductID) INNER JOIN SUPPLIER ON PRODUCT.SupplierID = SUPPLIER.SupplierID) GROUP BY SupplierName with ROLLUP