[fine] mysql joint primary key application

The joint primary key also plays an important role in taking care of the uniqueness of the data in the case of a large number of visits. The user can only evaluate the purchased product once. The self-incrementing ID of the evaluation is useless. The joint primary key composed of the user's ID and the product ID is much more meaningful.

CREATE TABLE `order_comment` (
  `user_id` int(11) NOT NULL DEFAULT '0',
  `order_id` int(11) NOT NULL DEFAULT '0',
  `name` varchar(30) NOT NULL,
  `address` varchar(60) NOT NULL,
  PRIMARY KEY (`user_id`,`order_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

 order item

CREATE TABLE `orders_items` (
  `order_id` int(11) DEFAULT '0' COMMENT 'Order ID',
  `product_id` int(11) DEFAULT '0' COMMENT '商品ID',
  `stock_name` varchar(80) DEFAULT '' COMMENT 'Commodity name',
  `stock_pre_price` decimal(10,2) DEFAULT '0.00' COMMENT 'Unit price of commodity',
  `stock_num` int(11) DEFAULT '0' COMMENT 'Number of items',
  PRIMARY KEY (`order_id`, `product_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;