CREATE TABLE TEST_TABLE (
    ID1 INTEGER,
    ID2 INTEGER,
    ID3 INTEGER
);
COMMIT;

INSERT INTO TEST_TABLE (ID1, ID2, ID3) VALUES (1, 1, NULL);
INSERT INTO TEST_TABLE (ID1, ID2, ID3) VALUES (1, 2, NULL);
INSERT INTO TEST_TABLE (ID1, ID2, ID3) VALUES (1, 3, NULL);
INSERT INTO TEST_TABLE (ID1, ID2, ID3) VALUES (2, 1, NULL);
INSERT INTO TEST_TABLE (ID1, ID2, ID3) VALUES (2, 2, NULL);
INSERT INTO TEST_TABLE (ID1, ID2, ID3) VALUES (2, 3, NULL);
COMMIT;

CREATE INDEX TEST_TABLE_IDX1 ON TEST_TABLE (ID1, ID2);
COMMIT;

select * from test_table where ID1 = 1 and ID2 = 2
-- one indexed read
select * from test_table where ID1 = 1 and ID2 IS NULL
-- zero indexed read

DROP INDEX TEST_TABLE_IDX1;
CREATE INDEX TEST_TABLE_IDX1 ON TEST_TABLE (ID1,ID2,ID3);

select * from test_table where ID1 = 1 and ID2 = 2
-- one indexed read again
select * from test_table where ID1 = 1 and ID2 IS NULL
-- 3(!!!) indexed reads