PostgreSQL changefeed using NOTIFY

psql_changefeed.sql

CREATE FUNCTION notify_changes() RETURNS trigger AS $$
DECLARE
BEGIN
  IF TG_OP = 'INSERT' THEN
    PERFORM pg_notify('insert', json_build_object('table', TG_TABLE_NAME, 'new_val', row_to_json(NEW))#>>'{}');
    RETURN NEW;
  ELSIF TG_OP = 'UPDATE' THEN
    PERFORM pg_notify('update', json_build_object('table', TG_TABLE_NAME, 'new_val', row_to_json(NEW), 'old_val', row_to_json(OLD))#>>'{}');
    RETURN NEW;
  ELSIF TG_OP = 'DELETE' THEN
    PERFORM pg_notify('delete', json_build_object('table', TG_TABLE_NAME, 'old_val', row_to_json(old))#>>'{}');
    RETURN OLD;
  END IF;
END;
$$ LANGUAGE plpgsql;


CREATE TRIGGER changefeed BEFORE INSERT OR UPDATE OR DELETE ON t
  FOR EACH ROW EXECUTE PROCEDURE notify_changes();