Imagine with me in this scenario that you lost the SYSTEM01.DBF DATAFILE which belongs to the SYSTEM TABLESPACE, what do you expect to happen of course the database will be closed automatically, even if the database remains open it must be closed immediately SHUT ABORT, as it is not conceivable that the database will work without the SYSTEM TABLESPACE, this scenario It also applies if we lose

the ACTIVE UNDO TABLESPACE.

Necessary steps:-

1- Close the database immediately if it remains open

SHUT ABORT;

2- Restore SYSTEM01.DBF from the last Backup.

3- Run the database in MOUNT mode.

STARTUP MOUNT;

4- RECOVERY the SYSTEM01.DBF DATAFILE.

ALTER DATABASE RECOVER AUTOMATIC DATAFILE 'D:\oradata\SYSTEM01.DBF';

5- Open the database.

ALTER DATABASE OPEN;

Note the difference between this scenario and the previous one. Here, the database must be closed before performing the recovery, unlike the previous scenario.