SELECT EmailAddress, SUM(ItemPrice)*Quantity AS TotalSum, SUM(DiscountAmount)*Quantity AS     TotalDiscount
FROM Customers JOIN Orders
ON Customers.CustomerID = Orders.CustomerID
JOIN OrderItems ON Orders.OrderID = OrderItems.OrderID
GROUP BY EmailAddress, ItemPrice, Quantity
ORDER BY TotalSum DESC;

SELECT
    EmailAddress,
    SUM(ItemPrice * Quantity) AS TotalSum,
    SUM(DiscountAmount * Quantity) AS TotalDiscount
FROM Customers
    JOIN Orders
        ON Customers.CustomerID = Orders.CustomerID
    JOIN OrderItems
        ON Orders.OrderID = OrderItems.OrderID
GROUP BY EmailAddress
ORDER BY TotalSum DESC;