题解 | #返回BR01 的产品的所有顾客的电子邮件（一）#
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
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'
)
)
-- 解法2；合并表解法，表较大时不推荐；但代码可读性高，表之间的关系也很清晰
SELECT cust_email
FROM Customers
JOIN Orders USING(cust_id)
JOIN OrderItems USING(order_num)
WHERE prod_id = 'BR01'
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