题解 | #返回每个顾客不同订单的总金额#

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

知识点：联结表

//注意一个cust_id可以对应多个order_num
group by cust_id	//而不是order_num