phpBB3 special ranks

SELECT  rank_id,  rank_title,  IFNULL(rank_owners, "-") AS rank_ownersFROM  phpbb3_ranksLEFT JOIN  (SELECT     GROUP_CONCAT(username ORDER BY username DESC SEPARATOR ', ') AS rank_owners,     user_rank   FROM phpbb3_users   GROUP BY user_rank) roON user_rank=rank_idWHERE rank_special=1;