题解 | #返回每个顾客不同订单的总金额#

1. 解题思路： 根据  OrderItems 查询 每组order_num所对应的产品总价，关联Orders查询 得到每个顾客每个订单的产品价格情况，最后根据顾客ID   cust_id分组，并计算每个顾客的金额总和，并最后按照总金额降序排列

select O2.cust_id ,
       sum(O1.amount) total_ordered  
  from (
    select order_num ,
           sum(item_price * quantity) amount 
      from OrderItems 
     group by order_num ) O1 
     join Orders O2 on O1.order_num = O2.order_num  
     group by O2.cust_id 
     order by total_ordered desc ;