题解 | #返回每个顾客不同订单的总金额#

select o.cust_id, sum(i.total_q) total_ordered from 
Orders o, (select order_num, sum(item_price*quantity) total_q from OrderItems group by order_num) i 
where o.order_num=i.order_num
group by cust_id 
order by total_ordered desc;