SELECT *
FROM
MYTAB A
WHERE
A.COL1 = :COL1
AND
A.COL2 = :COL2

SELECT *
FROM
MYTAB A
WHERE
(A.COL1 = :COL1 OR (A.COL1 IS NULL AND :COL1 IS NULL))
AND
(A.COL2 = :COL2 OR (A.COL2 IS NULL AND :COL2 IS NULL))