CREATE OR REPLACE FUNCTION message_store.cardinal_id(

stream_name varchar

) RETURNS varchar AS $$ DECLARE

_id varchar;

BEGIN

_id := id(cardinal_id.stream_name);

IF _id IS NULL THEN
  RETURN NULL;
END IF;

RETURN SPLIT_PART(_id, '+', 1);

END; $$ LANGUAGE plpgsql IMMUTABLE;