HOW OPEN RESETLOGS WITHOUT RECOVERY

Online redo logs are re-created . The log sequence is reset to 1.
If the databaseis running in archive log mode, the archived redo logs should then be deleted. Otherwise, chances are, that Oracle will eventually try to create an archived redo log whose file name already exists.
First i will show its Normal Database this mean not in recovery mode :
sqlplus / as sysdba
Connected to an idle instance.

SQL> ORACLE instance started.

Total System Global Area  838860800 bytes
Fixed Size                  2087672 bytes
Variable Size             213910792 bytes
Database Buffers          616562688 bytes
Redo Buffers                6299648 bytes
Database mounted.
Database opened.
SQL> shutdown
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> exit
Now Lets Open it :
sqlplus / as sysdba

Connected to an idle instance.

SQL> startup mount
ORACLE instance started.

Total System Global Area  838860800 bytes
Fixed Size                  2087672 bytes
Variable Size             213910792 bytes
Database Buffers          616562688 bytes
Redo Buffers                6299648 bytes
Database mounted.
SQL> alter database open resetlogs;
alter database open resetlogs
*
ERROR at line 1:
ORA-01139: RESETLOGS option only valid after an incomplete database recovery
SQL> recover database;
ORA-00283: recovery session canceled due to errors
ORA-00264: no recovery required


SQL> alter database open resetlogs;
alter database open resetlogs
*
ERROR at line 1:
ORA-01139: RESETLOGS option only valid after an incomplete database recovery


SQL> recover database until cancel;
Media recovery complete.
SQL> alter database open resetlogs;

Database altered.

Now the database is open, please do a clear database bounce.

Thanks!