如何使此mysql查询显示DISTINCT行？

Question

SELECT DISTINCT message_group.group_id, messages.*
FROM messages
LEFT JOIN message_group ON message_group.group_id = messages.group_id
WHERE message_group.username = 'admin'
OR message_group.recipients = 'admin'
ORDER BY messages.id DESC

Here is how it displays the data, even though I specified DISTINCT message_group.group_id

Why does it do this? How can I have it display only one group id ?

More reference: https://stackoverflow.com/questions/36167801/how-to-order-message-groups-messages-just-like-imessage

Answer 1

Try this:

SELECT message_group.group_id, messages.*
FROM messages INNER JOIN
    (SELECT 
        MAX(`timestamp`) AS latest,
        group_id
     FROM messages
     GROUP BY group_id) m2 
     ON messages.group_id = m2.group_id AND messages.`timestamp` = m2.`timestamp`
LEFT JOIN message_group ON message_group.group_id = messages.group_id
WHERE message_group.username = 'admin'
OR message_group.recipients = 'admin'
ORDER BY messages.id DESC