# 返回购买 prod_id 为BR01 的产品的所有顾客的电子邮件(Customers 表中的 cust_email) # 最内层的从 OrderItems 表返回 order_num,中间的从 Customers 表返回 cust_id。 SELECT c.cust_email FROM OrderItems oi,Orders o,Customers c WHERE oi.prod_id='BR01' AND oi.order_num=o.order_num AND o.cust_id=c.cust_id