Dual table default value? This link clear some of the queries about dual table.

But now I am having following doubt is the execution of two queries on dual table:

Query 1

Select * from dual; 


output:


D
-
X


Query2

Select NUll from dual;


output:


D
-



Does Dual contain default value as NULL? If yes why blank is not displayed, as in case of second query.
Phil has an interesting test case. But the dual table has one column and one row with the value x. When you select NULL from dual you are selecting a literal from a table. The literal is not actually in the table. That you can select sysdate from dual does not mean 
that sysdate is in the dual table either.


SQL> select sysdate from dual;

SYSDATE
---------------
23-MAY-14