How does 'in' clause works in oracle

Question

select \'true\' from dual where 1 not in (null,1);

when we execute this which will result nothing

what my question is:

is the above

Answer 1

The issue of your script in comparing with NULL value. You should use

column is null and column = 1

Actually NULL is an undefined value. Any comparation with NULL gives neither True nor False but NULL. Even NULL = NULL

That's why your 1 not in (null,1) doesn't work.