SELECT 
  vd.ref_event, 
  v.did, 
  v.kurzbeschr, 
  vd.timestamp 
FROM 
  veranstaltungen AS v 
  INNER JOIN veranstaltungen_daten AS vd ON v.did = vd.ref_event 
  LEFT JOIN veranstaltungen_daten AS vd2 ON v.did = vd2.ref_event AND vd.timestamp > vd2.timestamp
WHERE
  vd.timestamp >= unix_timestamp() 
  AND vd2.rid IS NULL
ORDER BY vd.timestamp