Accidentally you just added a datafile to the wrong directory or tablespace—a common error from even experienced DBA's. All is not lost; the datafile doesn't contain any data yet, so you can easily drop it, right?
Unfortunately, you can't. Prior to Oracle Database 10g Release 2, your only clean option for removing a datafile is to drop the entire tablespace and then rebuild it without that particular file. If the tablespace contains data, you have to go through the time-consuming and laborious process of storing the data on a separate location and reinstating it. In addition to its inconvenience, this process makes the tablespace unavailable.
Oracle Database 10g Release 2 the process has been simplified: You can just drop the datafile. For example, the following command will remove the indicated datafile from the tablespace as well as from the server.
alter tablespace users drop datafile '/tmp/users02.dbf'
There are a couple restrictions, however: The datafile must be empty to be dropped. You can't drop the last datafile in a tablespace; the tablespace itself must be dropped. And the tablespace must be online and in read-write status.
Oracle Data Files >