题解 | #返回每个顾客不同订单的总金额#

select 
    o.cust_id, -- 选择Orders表中的顾客ID 
    sum(oi.item_price * oi.quantity) as total_ordered -- 计算每个顾客所有订单的总金额  
from 
    Orders o
join
    OrderItems oi on oi.order_num = o.order_num -- 通过订单号将Orders表和OrderItems表进行连接
group by
    o.cust_id -- 按照顾客ID对结果进行分组，以便为每个顾客计算总金额 
order by
    total_ordered desc; -- 按照计算出的总金额降序排序结果