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,
    t1.order_num,
    t1.OrderTotal
from
    (
        select
            o1.order_num as order_num,
            o2.cust_id,
            sum(o1.quantity * o1.item_price) as OrderTotal
        from
            OrderItems o1
            left join Orders o2 on o1.order_num = o2.order_num
        group by
            o1.order_num,o2.cust_id
    ) t1
left join Customers c on t1.cust_id = c.cust_id
order by c.cust_name, t1.order_num

group by后面跟着的两个分组需要注意，如果不放就会报错