I have mistakenly added datafile to the tablespace... And was trying to drop it. I run the following:

```
alter database datafile 'datafile_name'  OFFLINE;

```

now when I run 

```
alter database datafile 'datafile_name'  ONLINE;

```

it shows 

```
ORA-01113: file 30 needs media recovery
ORA-01110: data file 30: 'datafile_name'

```

also status of the file is RECOVER... What can I do? I cant restart database....