This query can serve:
SELECT t.number, f.name
FROM ost_ticket t
JOIN ost_thread th ON (t.ticket_id = th.object_id)
LEFT JOIN ost_thread_entry e ON e.id =
(SELECT id
FROM ost_thread_entry
WHERE thread_id=th.id
AND TYPE='M'
LIMIT 1)
JOIN ost_attachment a ON ( e.id = a.object_id)
JOIN ost_file f ON (a.file_id = f.id)
ORDER BY t.number