php สอบถามการหาค่าอัตราการสั่งซื้อซ้ำ คิดเป็นร้อยละ

DROP PROCEDURE IF EXISTS `p_test`;
DELIMITER $$
CREATE DEFINER=`root`@`localhost` PROCEDURE `p_test`()

BEGIN
	SET @countOrder := (SELECT COUNT(`id`) FROM `order_header`);
	SELECT 
		a.`customer_name`,
		COUNT(b.`id`) AS `orders`,
		CONCAT(ROUND(((COUNT(b.`id`) / @countOrder) * 100),2),'%') AS `percentage`
	FROM
		`customer` a
	LEFT JOIN
		`order_header` b ON a.`id` = b.`customer_id`
	GROUP BY
		a.`id`
	ORDER BY
		a.`customer_name` ASC;
END $$
DELIMITER ;