MySQL选择范围内的值，该值不在另一个范围内

Posted 2021-04-07

我们有一个表格，我们记录每个客户的请求，每个请求得到一个created_at和customer_email列。

mysql> select * from requests;

+---------------------+-----------------------+
| created_at          | customer_email        |
+---------------------+-----------------------+
| 2016-08-08 14:05:50 | [e-mail]     |
| 2016-08-08 14:05:51 | [e-mail]     |
| 2017-08-15 14:41:40 | [e-mail]     |
| 2017-08-15 15:17:25 | [e-mail]     |
| 2018-08-15 15:30:41 | [e-mail]     |
+---------------------+-----------------------+

我想在08/2018获得customer email的created_at记录，但在此之前没有提出请求。换句话说，找出在08/2018创建请求的客户是新客户。 这是我正在尝试的查询，它返回0

    SELECT DISTINCT
    customer_email
FROM
    requests
WHERE
    created_at > '2018-08-01'
        AND customer_email NOT IN (SELECT DISTINCT
            customer_email
        FROM
            requests
        WHERE
            created_at < '2018-08-01')

任何帮助将非常感激！

答案

尝试GROUP BY与HAVING条款。

使用MIN函数，我们可以找到first_created_at的customer_email，然后利用HAVING子句，我们将结果集限制在08/18之后的first_created_at。

SELECT customer_email, DATE(MIN(created_at)) AS first_created_at 
FROM requests
GROUP BY customer_email 
HAVING first_created_at >= DATE('2018-08-01')