题解 |返回购买 prod_idBR01的所有顾客的电子邮件

where 简单联结：

select c.cust_email
from OrderItems a,Orders b,Customers c
where c.cust_id=b.cust_id 
	and a.order_num=b.order_num 
	and a.prod_id ='BR01'

inner join 内联结：

select c.cust_email
from Orders b   #注意以下两条件中b是公共的
inner join OrderItems a on a.order_num=b.order_num
inner join Customers c on c.cust_id=b.cust_id
where  a.prod_id ='BR01'