postgresql7.3
SELECT
b.subject AS subject,
b.message_id AS thread_id,
a.message_id AS message_id
FROM
(SELECT message_id, tree_sortkey, posting_date
FROM forums_messages
WHERE forum_id IN
(SELECT forum_id FROM forums_forums WHERE package_id = :package_id
and enabled_p = 't')
ORDER BY posting_date DESC LIMIT $n) a,
forums_messages b
WHERE
b.parent_id IS NULL
AND b.tree_sortkey = tree_root_key(a.tree_sortkey)
AND b.forum_id IN
(SELECT forum_id FROM forums_forums WHERE package_id = :package_id
and enabled_p = 't');
SELECT
subject, message_id
FROM
forums_messages_approved
WHERE
forum_id IN
(SELECT forum_id FROM forums_forums WHERE package_id = :package_id
and enabled_p = 't')
AND parent_id IS NULL
ORDER BY
posting_date DESC
LIMIT $n