Primary Key with Null Value...Amazing

Who said Primary key column cannot have null values...Here is a method you can create primary key with null values...

Create a table with null values.

create table tbl_null (a number);
insert into tbl_null values (null);
insert into tbl_null values (null);
insert into tbl_null values (null);
insert into tbl_null values (null);
commit;

select * from tbl_null;
4 rows selected

Now create a table with primary key column having null values..

Create table tbl_pri_null ( a primary key) as select * from tbl_null;
Table created

desc tbl_pri_null
Name - A
Null ? - Not Null
Type - Number

Select * from tbl_pri_null;
4 rows selected
All null values.....

Thats it. Folks!
Try and have fun....