Oracle 10gR2 : drop empty datafiles !

http://www.oracle.com/technology/pub/articles/10gdba/nanda_10gr2dba_part2.html

Drop Empty Datafiles
Imagine that you just added a datafile to the wrong directory or tablespace-a fairly common error. 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. Thankfully, in 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/users01.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.

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