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Asked: 2026-05-20T07:41:48+00:00

I am having problems selecting items from a table where a device_id can be

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I am having problems selecting items from a table where a device_id can be either in the from_device_id column or the to_device_id column. I am trying to return all chats where the given device is ID is in the from_device_id or to_device_id columns, but only return the latest message.

 select chat.*, (select screen_name from usr where chat.from_device_id=usr.device_id limit 1) as from_screen_name, (select screen_name from usr where chat.to_device_id=usr.device_id limit 1) as to_screen_name from chat where to_device_id="ffffffff-af28-3427-a2bc-83865900edbe" or from_device_id="ffffffff-af28-3427-a2bc-83865900edbe" group by from_device_id, to_device_id;


+----+--------------------------------------+--------------------------------------+---------+---------------------+------------------+----------------+
| id | from_device_id                       | to_device_id                         | message | date                | from_screen_name | to_screen_name |
+----+--------------------------------------+--------------------------------------+---------+---------------------+------------------+----------------+
| 20 | ffffffff-af28-3427-a2bc-83860033c587 | ffffffff-af28-3427-a2bc-83865900edbe | ee      | 2011-02-28 12:36:38 | kevin            | handset        |
|  1 | ffffffff-af28-3427-a2bc-83865900edbe | ffffffff-af28-3427-a2bc-83860033c587 | yyy     | 2011-02-27 17:43:17 | handset          | kevin          |
+----+--------------------------------------+--------------------------------------+---------+---------------------+------------------+----------------+
2 rows in set (0.00 sec)

As expected, two rows are returned. How can I modify this query to only return one row?

mysql> describe chat;
+----------------+---------------+------+-----+-------------------+----------------+
| Field          | Type          | Null | Key | Default           | Extra          |
+----------------+---------------+------+-----+-------------------+----------------+
| id             | int(11)       | NO   | PRI | NULL              | auto_increment |
| from_device_id | varchar(128)  | NO   |     | NULL              |                |
| to_device_id   | varchar(128)  | NO   |     | NULL              |                |
| message        | varchar(2048) | NO   |     | NULL              |                |
| date           | timestamp     | YES  |     | CURRENT_TIMESTAMP |                |
+----------------+---------------+------+-----+-------------------+----------------+
5 rows in set (0.00 sec)

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1 Answer

  1. Editorial Team
    select chat.*, 
       (select screen_name 
        from usr 
        where chat.from_device_id=usr.device_id
        limit 1
       ) as from_screen_name, 
       (select screen_name 
        from usr 
        where chat.to_device_id=usr.device_id
        limit 1
       ) as to_screen_name
from chat 
where to_device_id="ffffffff-af28-3427-a2bc-83865900edbe" or 
      from_device_id="ffffffff-af28-3427-a2bc-83865900edbe" 
group by from_device_id, to_device_id
order by date DESC
limit 1;

    You need to tell SQL that it should sort the returned data by date to get the most recent chat. Then you just limit the returned rows to 1.

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