题解 | #返回顾客名称和相关订单号以及每个订单的总价#

select
    cust_name,
    od.order_num,
    quantity * item_price as OrderTotal
from
    Orders od
    left join Customers ct on od.cust_id = ct.cust_id
    left join OrderItems odi on od.order_num = odi.order_num
# group by
#     ct.cust_name,
#     od.order_num
order by
    cust_name,
    od.order_num;
	
	这一题的表内容没有重复是不需要分组的，只需要通过两个左连接排序即可，如果数据有重复采用分组，那么Line4需要使用sum（）函数。