2. Make sure we have backups of all the datafiles. In RMAN type:
REPORT NEED BACKUP REDUNDANCY 1;

If there are datafiles that were not backed up as yet, there are 2 options:
a) delete the datafiles. (RMAN will create them and apply their data from redo logs).
b) issue RMAN command:
BACKUP DATAFILE N;

3. Use RMAN to restore and recover the datafile found missing in step #1. The recovery operation will fail because the online redo is missing.
RESTORE DATAFILE D;
RECOVER DATAFILE D;

4. Find the last log sequence:
SELECT SEQUENCE# FROM V$ARCHIVED_LOG WHERE RECID = (SELECT MAX(RECID) FROM V$ARC
HIVED_LOG);

5. Run the following RMAN script. The nunber X will be 1 more than the number you got from step 4. This is because the UNTIL SEQUENCE clause of RMAN goes to one less than the number specified.

RUN {
SET UNTIL SEQUENCE X THREAD 1;
RESTORE DATABASE;
RECOVER DATABASE;
ALTER DATABASE OPEN RESETLOGS;
}