text: ALTER TABLE room ADD COLUMN backend_id agent_id;
  
  ALTER TABLE room
  ADD CONSTRAINT room_backend_id_check
  CHECK (backend_id IS NULL OR backend = 'janus');
  
  UPDATE room AS r
  SET backend_id = rec.backend_id
  FROM rtc,
       recording AS rec 
  WHERE rtc.room_id = r.id
  AND   rec.rtc_id = rtc.id
  AND   r.backend = 'janus';
  
  ALTER TABLE recording DROP COLUMN backend_id;
  