现在这里有两个表：
stock_dismantle

stock_info

其中stock_dismantle中的后两个字段都是从stock_info的主键id中获取的，那么这时连表查询怎样才能同时找到stock_id_first和stock_id_second对应的stock_info里的信息呢？
要连两次表，并给表起别名

left JOIN stock_infor AS t1 ON stock_dismantle.stock_id_first = t1.id
left JOIN stock_infor AS t2 ON stock_dismantle.stock_id_second = t2.id

SELECT
	stock_dismantle.id,
	stock_dismantle.stock_id_first,
	stock_dismantle.stock_id_second,
	(
		SELECT
			t1.original_barcode
		WHERE
			t1.id = stock_dismantle.stock_id_first
	) AS aCode,
	(
		SELECT
			t2.original_barcode
		WHERE
			t2.id = stock_dismantle.stock_id_second
	) AS bCode,
	(
		SELECT
			t1.stock_name
		WHERE
			t1.id = stock_dismantle.stock_id_first
	) AS aName,
	(
		SELECT
			t2.stock_name
		WHERE
			t2.id = stock_dismantle.stock_id_second
	) AS bName,
(
		SELECT
			t1.stock_num
		WHERE
			t1.id = stock_dismantle.stock_id_first
	) AS aNum,
	(
		SELECT
			t2.stock_num
		WHERE
			t2.id = stock_dismantle.stock_id_second
	) AS bNum
FROM
	`stock_dismantle`
left JOIN stock_infor AS t1 ON stock_dismantle.stock_id_first = t1.id
left JOIN stock_infor AS t2 ON stock_dismantle.stock_id_second = t2.id

得到如下结果：

CREATE TABLE orderitems (
order_num int(11) NOT NULL,
order_item int(11) NOT NULL,
prod_id char(10) NOT NULL,
quantity int(11) NOT NULL,
item_price decimal(8,2) NOT NULL,
PRIMARY KEY (order_num,order_item),
KEY FK_OrderItems_Products (prod_id),
CONSTRAINT FK_OrderItems_Orders FOREIGN KEY (order_num) REFERENCES orders (order_num),
CONSTRAINT FK_OrderItems_Products FOREIGN KEY (prod_id) REFERENCES products (prod_id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;