Nemtom mennyire elegáns :)

SELECT kod,datum FROM (
SELECT ROWNUM rn,a.kod,a.datum,m FROM (SELECT kod,datum FROM BOLT b ORDER BY kod,datum
)a,(
SELECT kod,MAX(rn) m FROM (SELECT ROWNUM rn,kod,datum FROM (SELECT kod,datum FROM BOLT
ORDER BY kod,datum)) GROUP BY kod
) c WHERE a.kod = c.kod
) WHERE rn > m-4