题解 | #返回顾客名称和相关订单号以及每个订单的总价#

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

（常见的错误就是会漏掉后面两个字段，一旦使用group by聚合了，select和order by后面的所有非聚合字段，都要用group by聚合一下，这里有没有sum函数都一样，sum（）属于聚合字段，不影响）

来自~见解