题解 | SQL必知必会 T97

select
    c.cust_name,
    o.order_num,
    sum(oi.item_price * oi.quantity) OrderTotal
from
    Orders o
    inner join Customers c on c.cust_id = o.cust_id
    inner join OrderItems oi on o.order_num = oi.order_num
group by
  o.order_num,
  c.cust_name
order by
    cust_name asc,
    o.order_num asc

思路：

1.三张表中orders表的变量能够分别在其他两张表中找到对应的，所以将其他两张表加入到orders中来写比较容易理解。

2.加总的时候，要注意按照订单号order_num与人名，不然会出现加总错误。

3.先group后order。先排序的放在前面。