Why this Query Returns null

Why this query returns null? Why rownum does not work with equality?

select * from emp where rownum = 10;

SQL> select rowid,rownum from emp ;
ROWID ROWNUM
------------------ ----------
AAAHcIAABAAAMuiAAA 1
AAAHcIAABAAAMuiAAB 2
AAAHcIAABAAAMuiAAC 3
AAAHcIAABAAAMuiAAD 4
AAAHcIAABAAAMuiAAE 5
AAAHcIAABAAAMuiAAF 6
AAAHcIAABAAAMuiAAG 7
AAAHcIAABAAAMuiAAH 8
AAAHcIAABAAAMuiAAI 9
AAAHcIAABAAAMuiAAJ 10
AAAHcIAABAAAMuiAAK ! 11

ROWID ROWNUM
------------------ ----------
AAAHcIAABAAAMuiAAL 12
AAAHcIAABAAAMuiAAM 13
AAAHcIAABAAAMuiAAN 14
AAAHcIAABAAAMuiAAO 15
AAAHcIAABAAAMuiAAP 16
16 rows selected.

SQL> select * from emp where rowid='AAAHcIAABAAAMuiAAJ' ;
EMPNO ENAME JOB MGR HIREDATE SAL COMM
---------- --------------- --------- ---------- --------- ---------- ----------
DEPTNO
----------
7844 TURNER SALESMAN 7698 08-SEP-81 1500 0
30

What I inquire is only this rowid is changed to rownumber for the userfriendly environment..and in order to retrieve it we should use only this rowid..This is what i feel and i may be right or wrong.just want to share what i feel.

.............

Rownum is not stored in database, it is a pseudocolumn, and generated only when we try to retrieve data from the tables. oracle assigns the sequential number in the same order it retrieves the records from the table.

Now if you use "<" then oracle can find out the records rownum and returns the records. while in case of equality, its not possible to identify a record order in which it is going to be returned.

.........

Its wrong query

select * from emp where rownum = 10;

Right query is : select * from emp where (cloumn name) = 10;

...............

To remove duplicate rows using rownum, do the following:

select rownum, ...column name.. from ...table name..;

you will get the list of records with unique rownum. Even the duplicate records will have different rownum.

Now, you can use the DELETE statement to remove one of the duplicate record.

delete ....table name.. where rownum= X; ( where X is the rownum of the duplicate record)

Hope you have understood!!!