GO
CREATE TRIGGER update_amount_sell ON tblHas after INSERT AS
BEGIN
    UPDATE tblSell
    SET tblSell.amount = tblSell.amount - (
        SELECT amount
        FROM inserted
        WHERE idShop = tblSell.idShop AND idProduct = tblSell.idProduct
    )
    FROM tblSell
    JOIN inserted ON tblSell.idProduct = inserted.idProduct AND tblSell.idShop = inserted.idShop
END