Oracle Database Discussions

Hello guys,
i tested something around with B-Tree indexes and NULL values in columns.

Here is a little test scenario.
----------------------------------------------------------------------------------------------------------------
create table INDEX_TEST (
F0 NUMBER,
F1 VARCHAR2(20),
F2 VARCHAR2(20),
F3 NUMBER);
BEGIN
FOR i in 1 .. 200 LOOP
INSERT INTO INDEX_TEST VALUES(i,NULL,NULL,NULL);
END LOOP;
COMMIT;

END;

CREATE INDEX INDEX_TEST_01 ON INDEX_TEST(F0);
CREATE INDEX INDEX_TEST_02 ON INDEX_TEST(F0,F1);
CREATE INDEX INDEX_TEST_03 ON INDEX_TEST(F1);
----------------------------------------------------------------------------------------------------------------

After that i block dumped the indeces and have a look at null values in the leaf blocks.

At first i looked at index INDEX_TEST_01 which has only one column, but in the leaf block there are 2 columns... have a look - for example:
row#131[6416] flag: ------, lock: 0, len=13
col 0; len 3; (3): c2 02 21
col 1; len 6; (6): 01 80 41 6f 00 83

After that i have a look at the index INDEX_TEST_02, and there are 3 columns in the index leaf block dump... but the index has only 2 columns:
row#131[6284] flag: ------, lock: 0, len=14
col 0; len 3; (3): c2 02 21
col 1; NULL
col 2; len 6; (6): 01 80 41 6f 00 83

It was interesting that a NULL value was stored in the index, even if oracle says that NULL values are not indexed.
Oracles statement with NULL values is correct in case of the index INDEX_TEST_03, there was no NULL value indexed... even tgough i put in some value to column F1. Only the non NULL values of F1 were stored in the index.

My question to you:
Why is there one more column in the leaf block dump as in the index definition? Is there any plausible cause?

Thanks and Regards
Stefan