Postgres: Проверка целостности, генерация исключения

CREATE OR REPLACE FUNCTION client.fx_check_admin_id(admin_id integer)
  RETURNS integer AS
$BODY$
--
-- Проверка admin_id
--
BEGIN
    IF NOT (EXISTS(SELECT client.admins.admin_id
        FROM client.admins WHERE client.admins.admin_id=$1 LIMIT 1)) THEN
            RAISE EXCEPTION 'Admin with admin_id="%" not exists!', $1;
    END IF;
    RETURN 1;
END
-- eof
$BODY$
  LANGUAGE 'plpgsql' IMMUTABLE SECURITY DEFINER
  COST 100;
ALTER FUNCTION client.fx_check_admin_id(integer) OWNER TO sk4_admin;
GRANT EXECUTE ON FUNCTION client.fx_check_admin_id(integer) TO sk4_admin;
GRANT EXECUTE ON FUNCTION client.fx_check_admin_id(integer) TO public;