ขอแนวคิดเรื่อง sql การ query หน่อย ครับ ว่ามีทางที่ดีกว่านี้หรือป่าว

CREATE TABLE IF NOT EXISTS `product` (
  `product_id` int(10) NOT NULL AUTO_INCREMENT,
  `cate_id` varchar(10) NOT NULL,
  `product_name` varchar(50) NOT NULL,
  `product_detail` varchar(100) NOT NULL,
  `product_total` int(5) NOT NULL,
  `product_size` varchar(100) NOT NULL,
  `product_price` decimal(10,2) NOT NULL,
  `product_date` date NOT NULL,
  `product_pic` varchar(50) NOT NULL,
  PRIMARY KEY (`product_id`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=46 ;

CREATE TABLE IF NOT EXISTS `order_detail` (
  `order_detail_id` int(10) NOT NULL AUTO_INCREMENT,
  `order_id` varchar(10) NOT NULL,
  `product_id` varchar(10) NOT NULL,
  `amount` int(3) NOT NULL,
  `size` varchar(10) NOT NULL,
  PRIMARY KEY (`order_detail_id`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=29 ;

CREATE TABLE IF NOT EXISTS `order` (
  `order_id` varchar(10) NOT NULL,
  `pay_status` varchar(10) NOT NULL,
  `tran_status` varchar(2) NOT NULL,
  `cus_id` varchar(10) NOT NULL,
  `order_date` date NOT NULL,
  `order_know` varchar(1) NOT NULL,
  `order_summary` decimal(10,2) NOT NULL,
  PRIMARY KEY (`order_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

SELECT product_id,order_date , sum( b.amount ) AS sum_total FROM `order` a INNER JOIN `order_detail` b ON a.order_id = b.order_id WHERE order_date LIKE '$yy-$mm-%' GROUP BY b.product_id ORDER BY sum_total desc