-- 三表联结：等联结法
select cust_name,order_num,sum(quantity*item_price) as OrderTotal
from(
    select Customers.cust_name cust_name,
    OrderItems.*
    from Customers,Orders,OrderItems
    where Customers.cust_id=Orders.cust_id and Orders.order_num=OrderItems.order_num
    
) temp 
group by cust_name,order_num
order by cust_name,order_num