题解 | #返回每个顾客不同订单的总金额#

-- 思路：先根据OrderItems查出每个order_num的总金额，将查出的表和Orders表内连接，连接后查每个cust_id的总金额
select
    cust_id,
    sum(o_total) as total_ordered
from
    (
        select
            order_num,
            sum(item_price * quantity) as o_total
        from
            OrderItems
        group by
            order_num
    ) as temp
    inner join Orders on temp.order_num = Orders.order_num
group by
    cust_id
order by
    total_ordered desc;