SELECT f.`name`, f.`safe_name`, f.`id`, t.`id`,t.`title`, t.`updated`, u.`name` as last_user, t.`date`
FROM `kb_forums` f 
LEFT OUTER JOIN `kb_topics` t
ON t.`forumid` = f.`id`
LEFT OUTER JOIN `kb_users` u
ON t.`userid` = u.`id`
WHERE f.`catid` = '1' 
ORDER BY f.`posid` ASC, t.`updated` DESC