题解 | #返回购买 prod_id 为 BR01 的产品#

select `cust_email`
 from `OrderItems` o1, `Orders` o2, `Customers` o3
 where `prod_id`='BR01' and o1.order_num=o2.order_num and o2.cust_id=o3.cust_id

select `cust_email`
from `Customers`
where `cust_id` in (select `cust_id`
                    from `Orders`
                    where `order_num` in (select `order_num`
                                          from `OrderItems`
                                          where `prod_id`='BR01'))