Backup/Recover datafile doubts..Please help

Hi ,

I had backed a Oracle dbf file using backup / restore commands of Unix and restored from tape with unix command. Then from the Oracle Server Manager I put the file into the database but
it resulted in Media failure.
Perhaps due to data corruption.
I did "alter database <database name>

             recover datafile <path where the datafile has been copied" On doing this the database got connected. Since I am not a DBA I have these set of doubts : Now , my doubts are how has this "alter database ..." command helped in correcting the restored dbf file.
But, my DBA friend told me that "alter database ..." command has helped the newer
restored file in getting seq with Ctrl and database file , is it right ?

If yes ,, please tell me how.

I also got information like it is mandatory process to do "alter database ..." command
after recovering dbf files from tapes or any archive device. Is this also true ?

Thanks ,
Vidya Received on Mon Nov 22 1999 - 00:00:00 CET