SELECT i.id_predmeta, i.oznaka_roka, i.godina_roka
FROM ispit i
WHERE i.ocena > 5 AND i.status_prijave = 'o'
AND COALESCE(i.datum_usmenog, i.datum_pismenog) =
    (SELECT MAX(COALESCE(datum_usmenog, datum_pismenog))
    FROM ispit
    WHERE id_predmeta = i.id_predmeta
    AND ocena > 5 AND status_prijave = 'o'));

SELECT i.id_predmeta, i.oznaka_roka, i.godina_roka
FROM ispit i
WHERE i.ocena > 5 AND i.status_prijave = 'o'
AND NOT EXISTS(SELECT * FROM ispit
                WHERE id_predmeta = i.id_predmeta
                AND ocena > 5 AND status_prijave = 'o'
                AND COALESCE(datum_usmenog, datum_pismenog) >
                    COALESCE(i.datum_usmenog, i.datum_pismenog));