Try this:
PHP Code:
$getusers = $vbulletin->db->query("
SELECT COUNT(p.postid) AS total, p.userid, u.username, u.joindate, f.field7
FROM " . TABLE_PREFIX . "post AS p
LEFT JOIN " . TABLE_PREFIX . "user AS u USING (userid)
LEFT JOIN " . TABLE_PREFIX . "userfield AS f USING (userid)
WHERE p.dateline > $cutoffstart
AND p.dateline < $cutoffend
GROUP BY userid
ORDER BY total DESC
LIMIT $limit
");