题解 | 返回顾客名称和相关订单号以及每个订单的总价
select a.cust_name, b.order_num, sum(quantity * item_price) OrderTotal from Customers a inner join Orders b on a.cust_id = b.cust_id inner join OrderItems c on c.order_num = b.order_num group by cust_name, order_num order by cust_name, order_num;