题解 | #确定最佳顾客的另一种方式（二）#

# 方法1：内连接
select  c.cust_name,sum(oi.quantity*oi.item_price)total
from Customers c,Orders o,OrderItems oi
where c.cust_id=o.cust_id
and o.order_num=oi.order_num
group by  c.cust_name
having total>=1000;

# 方法2：先筛选后链接
select c.cust_name,cus_total.total
from orders o,
     customers c ,
     (select order_num,sum(item_price*OrderItems.quantity)total
        from orderitems
        group by order_num
      having sum(item_price*OrderItems.quantity)>=1000) as cus_total
where cus_total.order_num=o.order_num
and o.cust_id=c.cust_id;