So, habs nun endlich gelöst
Danke an alle ^^

Hier die Lösung:

Code:
select * 
from studienleistung 
where ects = ( SELECT ects
               FROM (SELECT ects, ROWNUM rn
                     FROM (SELECT distinct ects
                           FROM studienleistung
                           WHERE ects IS NOT NULL
                           ORDER BY ects DESC)
                     WHERE ROWNUM <= 5)
               WHERE rn = 5)
;