dual table - 9iR2

I am curious about the behavior of dual table in oracle 9iR2 . It looks like when selecting from dual, implicitly where rownum=1 is added . I am just curious about how it works .

Connected to:
Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production With the Partitioning and OLAP options
JServer Release 9.2.0.4.0 - Production

SQL> select count(*) from dual;

  COUNT(*)

         1

SQL> select * from dual;

D
-

X

SQL> insert into dual values('Y');

1 row created.

SQL> commit;

Commit complete.

SQL> select * from dual;

D
-

X

SQL> select count(*) from dual;

  COUNT(*)

         2

SQL> set head off
SQL> /          2

SQL> select * from dual;

X

SQL> insert into dual values('Z');

1 row created.

SQL> select * from dual;

X

SQL> commit;

Commit complete.

SQL> select count(*) from dual;

         3

SQL> select * from ( select * from dual) ;

X Received on Tue Sep 14 2004 - 21:22:34 CDT