v PL SQL:
SELECT ID, poradi, datum
FROM tab
WHERE poradi = (SELECT MAX(poradi) FROM tab WHERE datum IS NOT NULL)
UNION
SELECT ID, poradi, datum
FROM tab
WHERE poradi = (SELECT min(poradi) FROM tab WHERE datum IS NULL)
;
v PL SQL:
SELECT ID, poradi, datum
FROM tab
WHERE poradi = (SELECT MAX(poradi) FROM tab WHERE datum IS NOT NULL)
UNION
SELECT ID, poradi, datum
FROM tab
WHERE poradi = (SELECT min(poradi) FROM tab WHERE datum IS NULL)
;