题解 | 返回顾客名称和相关订单号以及每个订单的总价

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

先用一个临时的结果集来存储OrderTotal的结果，然后三个表都用join连接起来（要注意的是total_OrderItems不能写成to，因为这是SQL中的关键字）