Get info for multiple users in thread topic

SELECT u.`name`, u.`signature`, u.`rank`, COUNT(*) as numPosts
FROM `users` u INNER JOIN `posts` p ON (u.`id` = p.`userId`)
WHERE u.`id` IN (
    SELECT `userId` FROM `posts` WHERE `threadId` = 5
)
GROUP BY u.`name`, u.`signature`, u.`rank`