题解 | #返回顾客名称和相关订单号以及每个订单的总价#

/*多表联结，分别通过相同的列将表关联起来，当中的select子句
相当于另外创建了一张表oo。
在不影响速度情况下，join可以多次使用
*/
select c.cust_name, oo.order_num, oo.OrderTotal
from Orders o
join
(select order_num, sum(quantity * item_price) OrderTotal
from OrderItems 
group by order_num) oo
on oo.order_num = o.order_num
join Customers c
on c.cust_id = o.cust_id
order by c.cust_name, oo.order_num;