CREATE OR REPLACE FUNCTION czyBiletPosiadaKlienta(id_bilet integer)
RETURN number IS
   czyID INTEGER;
BEGIN
   SELECT ID_KLIENTA into czyID
   FROM BILETY
   WHERE ID = id_bilet;
   RETURN czyID;

EXCEPTION
   WHEN NO_DATA_FOUND THEN
    dbms_output.put_line('Blad');
END;