select cust_email from Customers join Orders using(cust_id) where order_num in ( select order_num from OrderItems join Orders using(order_num) where prod_id = 'BR01' ) 1、使用join,根据关联字段来连接2、使用子查询的好处:不用一次把所有的连接关系写完,每次只需要关注两种表的链接。ps:Customers 和 Orders 只需要关注公共字段 cust_id , 然后后续根据order_num去关联其...