只能说：简单易懂 将查询第一个表的结果组合成第三个表 通过order_num联结第二个表和第三个表 select cust_id,total_ordered from Orders,( select order_num,sum(item_price*quantity) as total_ordered from OrderItems group by order_num order by total_ordered )as tot where Orders.order_num=tot.order_num order by total_ordered de...