HELP - UNRECOVERABLE DATAFILE

DBA's,

Please helpme understand this:

ALTER DATABASE CLEAR LOGFILE GROUP 1 UNRECOVERABLE DATAFILE;

As I understand this, this command is used to clear a log file needed by an offline datafile for recovery and that offline datafile will be unusable after issuing this command.

1. If a datafile is offline how will grnerate redo information?
2. And in case it is issued, how do you bring the datafile online?

Thanks,
Nizar

This statement is used to clear a logfile when a datafile as been taken offline during the recovery process. As you say, if the datafile is taken offline during normal operation, no redo will get generated.