返回购买prod_id为BR01 的产品的所有顾客的电子邮件
返回购买 prod_id 为 BR01 的产品的所有顾客的电子邮件（一）
https://www.nowcoder.com/practice/962b16554fbf4b99a87f4d68020c5bfb
方法一:
SELECT
cust_email
FROM
Customers AS C
LEFT JOIN Orders AS O ON C.cust_id = O.cust_id
LEFT JOIN OrderItems AS ot ON ot.order_num = O.order_num
WHERE
ot.prod_id = 'BR01';
方法二:
SELECT
cust_email
FROM
Customers
WHERE
cust_id in (
SELECT
cust_id
FROM
Orders
WHERE
order_num IN (
SELECT
order_num
FROM
OrderItems AS ot
WHERE
ot.prod_id = 'BR01'
)
)
