$sql = "SELECT SQL_NO_CACHE p1.* FROM comment p1 INNER JOIN
      (SELECT max(seen) last_seen, max(id) MaxId,
      user_id, topic_id, picture_id, news_id, date
      FROM comment WHERE user_id='$me' and deleted=0
      GROUP BY topic_id) p2
   ON p1.topic_id = p2.topic_id
   WHERE p1.date > p2.last_seen and p1.id > p2.MaxId and deleted=0
   GROUP BY p1.topic_id ORDER BY p1.date DESC"

$sql = "SELECT SQL_NO_CACHE p1.* FROM comment p1 INNER JOIN
      (SELECT max(seen) last_seen, max(id) MaxId,
      user_id, topic_id, picture_id, news_id, date
      FROM comment WHERE user_id='$me' and deleted=0
      GROUP BY topic_id, picture_id, news_id) p2
   ON p1.topic_id = p2.topic_id and p1.picture_id= p2.picture_id
   and p1.news_id= p2.news_id
   WHERE p1.date > p2.last_seen and p1.id > p2.MaxId and deleted=0
   GROUP BY p1.topic_id, p1.picture_id, p1.news_id ORDER BY p1.date DESC"

CREATE TABLE `comment` (
`id` int(11) NOT NULL,
`user_id` int(11) NOT NULL,
`topic_id` int(11) NOT NULL,
`picture_id` int(11) NOT NULL,
`news_id` int(11) NOT NULL,
`text` text COLLATE utf8_hungarian_ci NOT NULL,
`date` datetime NOT NULL,
`reply_id` int(11) NOT NULL,
`comment_vote` int(11) NOT NULL,
`comment_hit` int(11) NOT NULL,
`moderated` int(11) NOT NULL,
`seen` datetime NOT NULL,
`deleted` tinyint(4) NOT NULL,
`ip` text COLLATE utf8_hungarian_ci NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8
COLLATE=utf8_hungarian_ci;

1(id)   PRIMARY(select_type)    <derived2>(table) ALL(type) NULL(possible keys) NULL(key)   NULL(key_len)   NULL(ref)   105(rows)   Using temporary; Using filesort(extra)
1(id)   PRIMARY(select_type)    p1(table)   ref(type)   PRIMARY,topic_id,deleted,date,picture_id,news_id(possible keys)  topic_id(key)  4(key_len)  p2.deck_id(ref) 5(rows) Using where(extra)
2(id)   DERIVED(select_type)    p2(table)   index_merge(type)   deleted,user_id(possible_keys)  user_id(key)    4,1(key_len)    NULL(ref)   169(rows)   Using intersect(user_id,deleted); Using where; Using filesort(extra)