似乎您没有为每条消息填写用户和头像.

Seems you don't have users and avatars filled for each message.

尝试将INNER JOINS替换为OUTER JOINS.

SELECT  t.topicname, m. *, ms.avatar
FROM    `messages` m
JOIN    topics t
ON      t.topicid = m.topicid
LEFT JOIN
        users u
ON      u.username = m.author
LEFT JOIN
        misc ms
ON      ms.userid = u.userid
ORDER BY
        m.postdate DESC
LIMIT 5