题解 | #返回购买 prod_id 为 BR01 （二）#

# select
#     cust_email
# from
#     Customers 
#     inner join Orders on Customers.cust_id = Orders.cust_id
#     inner join OrderItems on OrderItems.order_num = Orders.order_num
# where prod_id = 'BR01'

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'  
)
)

多层子查询

从上往下写，发现和别的表关联的字段就使用（select x from 表 where 另外一个字段xx in ()）