我要选择包含不同电子邮件的行，请参见下面的示例表：
表名=用户
SESSION_COOKIE_DOMAIN所需的结果将是：
+----+---------+-------------------+-------------+
| id | title | email | commentname |
+----+---------+-------------------+-------------+
| 3 | test | rob@hotmail.com | rob |
| 4 | i agree | rob@hotmail.com | rob |
| 5 | its ok | rob@hotmail.com | rob |
| 6 | hey | rob@hotmail.com | rob |
| 7 | nice! | simon@hotmail.com | simon |
| 8 | yeah | john@hotmail.com | john |
+----+---------+-------------------+-------------+
不同的值应该是表示例 +----+-------+-------------------+-------------+
| id | title | email | commentname |
+----+-------+-------------------+-------------+
| 5 | its ok| rob@hotmail.com | rob |
| 7 | nice! | simon@hotmail.com | simon |
| 8 | yeah | john@hotmail.com | john |
+----+-------+-------------------+-------------+
中的最新条目
所需的SQL是什么？
答案 0 :(得分：4)
如果您使用的是MySQL 5.7或更早版本，则可以将表加入一个子查询，该子查询查找每封电子邮件的最新记录：
2019-01-21 10:08:50 INFO m.d.s.a.b.reader.PortalMessageReader - Portal Message Read by Thread id 115 - Thread name: poller_batch_thread115
2019-01-21 10:08:50 INFO m.d.s.a.b.reader.PortalMessageReader - Portal Message Read by Thread id 116 - Thread name: poller_batch_thread116
如果您使用的是MySQL 8+，则只需在此处使用SELECT t1.id, t1.title, t1.email, t1.commentname
FROM yourTable t1
INNER JOIN
(
SELECT email, MAX(id) AS latest_id
FROM yourTable
GROUP BY email
) t2
ON t1.email = t2.email AND t1.id = t2.latest_id;
：
ROW_NUMBER注意：您的预期输出可能有问题，并且WITH cte AS (
SELECT id, title, email, commentname,
ROW_NUMBER() OVER (PARTITION BY email ORDER BY id DESC) rn
FROM yourTable
)
SELECT id, title, email, commentname
FROM cte
WHERE rn = 1;
记录是id = 6的最新记录。
答案 1 :(得分：1)
您可以在下面使用相关子查询尝试
select * from table1 a
where id in (select max(id) from table1 b where a.email=b.email group by b.email)
答案 2 :(得分：0)
如果'id'是唯一键或主键，则可以使用此键：
select * from Users where id in (select max(id) from Users group by commentname)
以上所述将提高数据库性能，因为correlated subqueries来自以下事实：子查询使用外部查询的信息，并且子查询对外部查询的每一行执行一次。因此，我建议您使用如果“ id”是唯一的，我的回答是。