题解 | 返回顾客名称和相关订单号以及每个订单的总价

select
    c.cust_name,
    os.order_num,
    sum(os.quantity * os.item_price) OrderTotal
from
    Orders o
    join OrderItems os on os.order_num = o.order_num
    join Customers c on c.cust_id = o.cust_id
group by
    c.cust_name,
    os.order_num
order by
    c.cust_name,
    os.order_num;