sys_op_map_nonnull

http://www.oracledba.co.uk/tips/sys_op_map_nonnull.htm
Undocumented Oracle

CREATE TABLE t (
col1 VARCHAR2(20),
col2 VARCHAR2(20))
TABLESPACE data_sml;

INSERT INTO t VALUES ('ABC', 'ABC');　　　①
INSERT INTO t VALUES ('ABC', 'ABc');　　　②
INSERT INTO t VALUES ('123', NULL);　　　③
INSERT INTO t VALUES ('TRUE', 'FALSE');　④
COMMIT;

SELECT *
FROM t
WHERE sys_op_map_nonnull(col1) = sys_op_map_nonnull(col2);
→①だけが選択される