SELECT COUNT( id ) AS `cnt`, ROUND( SUM( vote ) / COUNT( id ) , 5 ) AS `vote`
                       FROM `test419_pmf_topic_rating`
                       WHERE`topic_id` =8
                       GROUP BY `topic_id`

phpMyForum (http://pmf-test.j-remmer.de/index.php)
-- Kategorie - Test (http://pmf-test.j-remmer.de/board.php?id=2)
---- Forum 2 - Test (http://pmf-test.j-remmer.de/board.php?id=5)
------ Unterforum - Test (http://pmf-test.j-remmer.de/board.php?id=11)
Thema: test 21.04.2012 (http://pmf-test.j-remmer.de/topic.php?id=8)