题解 | 返回顾客名称和相关订单号以及每个订单的总价

select 
    cust_name,
    o1.order_num as order_num,
    sum(quantity*item_price) as OrderTotal
from OrderItems o1
join Orders o2 on o1.order_num=o2.order_num
join Customers c on o2.cust_id=c.cust_id
group by 1,2
order by 1,2;