Julian, 1) Am I right this transformation is not performed for sane queries? By "sane" I mean the ones that have not null constraints and/or "where" conditions.
2) I just did a quick check and "() not in ()" is positive while "(null) not in (null)" is negative. select * from dual where (select * from dual where 1=2) not in (select * from dual where 1=2); <-- returns a row select * from dual where (null) not in (null); <-- returns no rows Vladimir
