DELIMITER //
CREATE TRIGGER updateTotalPrice AFTER INSERT ON `OrderLine` FOR EACH ROW
    BEGIN
        UPDATE `CustomOrder`
            SET `TotalPrice` = `TotalPrice` + (
                SELECT a.`Price`*ol.`Amount` FROM `Article` a WHERE a.`Nr` = NEW.`ArtNr`
            )
        WHERE `Nr` = NEW.`OrderNr`;
    END //
DELIMITER ;