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,
    c.OrderTotal
from 
    Customers a
left join
    Orders b on a.cust_id = b.cust_id
left join 
    (
        select
            order_num,
            sum(quantity * item_price) as OrderTotal
        from 
            OrderItems
        group by 
            1
    ) c on b.order_num = c.order_num
order by 
    1,2