Something

$sql = $link->query("SELECT blog_messages.*, users.firstname AS author, COUNT(comments.id) AS ncomments FROM blog_messages "
				  . "LEFT JOIN admin_users AS users ON blog_messages.author = users.id "
				  . "LEFT JOIN blog_comments AS comments ON blog_messages.id = comments.pid "
				  . "GROUP BY blog_messages.id "
				  . "ORDER BY id DESC LIMIT 5");