gistfile1.sql

SELECT `forum`.`ID`, `forummeta`.`meta_value`, `group`.`id`
FROM `wp_posts` AS `forum`
LEFT JOIN `wp_postmeta` AS `forummeta`
ON `forum`.`ID` = `forummeta`.`post_id`
AND `forummeta`.`meta_key` = '_bbp_old_forum_id'
LEFT JOIN `wp_bp_groups` AS `group`
ON `group`.`slug` = `forum`.`post_name`
WHERE `forum`.`post_type` = 'forum' AND `group`.`id` > 0
GROUP BY `forum`.`ID`;