Unknown column 't.last_datetime' in 'field list' SELECT t.id,t.userid,t.nickname,t.subject,t.replys,t.browse,FROM_UNIXTIME(t.last_datetime) AS last_datetime FROM bbs_topics AS t LEFT JOIN group_joins AS j ON t.userid = j.userid WHERE j.group_id = 5 AND j.is_unchecked <> 1 ORDER BY t.last_datetime DESC LIMIT 0, 12