CREATE TRIGGER Questao4
ON [ORDER Details] FOR INSERT, UPDATE
AS
IF NOT UPDATE (Discount)
BEGIN
    UPDATE od
    SET od.Discount = 0.01 * t.qtdProdutos
    FROM [ORDER Details] od JOIN Orders o1
    ON od.OrderID = o1.OrderID JOIN
    (
    SELECT CustomerID, ProductID, COUNT(*) AS qtdProdutos
    FROM Orders o2 JOIN [ORDER Details] od
    ON o.orderID = od.OrderID
    WHERE EXISTS(
        SELECT *
        FROM Inserted i JOIN Orders o3
        ON i.OrderID = o3.OrderID
        WHERE o.OrderID < i.OrderID
        AND o2.CustomerID = o3.Customer
        )
    GROUP BY CustomerID, ProductID
    ) t ON o1.CustomerID = t.CustomerID
    AND od.ProductID = t.ProductID
END