怎么从tablsespace 里面删除一个datafile?

sqlcode

How to 'DROP' a Datafile from a Tablespace:
===========================================

Before we start with detailed explanations of the process involved, please note
that Oracle does not provide an interface for dropping datafiles in the same
way that you could drop a schema object such as a table, a view, a user, etc.  
Once you make a datafile part of a tablespace, the datafile CANNOT be removed,
although we can use some workarounds.

Before performing certain operations such as taking tablespaces/datafiles
offline, and trying to drop them, ensure you have a full backup.

If the datafile you wish to remove is the only datafile in that tablespace,
simply drop the entire tablespace using:

    DROP TABLESPACE <tablespace name> INCLUDING CONTENTS;

You can confirm how many datafiles make up a tablespace by running the
following query:

    select file_name, tablespace_name
    from dba_data_files
    where tablespace_name ='<name of tablespace>';

The DROP TABLESPACE command removes the tablespace, the datafile, and the
tablespace's contents from the data dictionary.  Oracle will no longer have
access to ANY object that was contained in this tablespace.  The physical
datafile must then be removed using an operating system command (Oracle NEVER
physically removes any datafiles).  Depending on which platform you try this
on, you may not be able to physically delete the datafile until Oracle is
completely shut down. (For example, on Windows NT, you may have to shutdown
Oracle AND stop the associated service before the operating system will allow
you to delete the file - in some cases, file locks are still held by Oracle.)

If you have more than one datafile in the tablespace, and you do NOT need the
information contained in that tablespace, or if you can easily recreate the
information in this tablespace, then use the same command as above:

    DROP TABLESPACE <tablespace name> INCLUDING CONTENTS;

Again, this will remove the tablespace, the datafiles, and the tablespace's
contents from the data dictionary.  Oracle will no longer have access to ANY
object that was contained in this tablespace.  You can then use CREATE
TABLESPACE and re-import the appropriate objects back into the tablespace.

If you have more than one datafile in the tablespace and you wish to keep the
objects that reside in the other datafile(s) which are part of this tablespace,
then you must export all the objects  inside the affected tablespace.  Gather
information on the current datafiles within the tablespace by running this
query:

    select file_name, tablespace_name
    from dba_data_files
    where tablespace_name ='<name of tablespace>';

Make sure you specify the tablespace name in capital letters.

In order to allow you to identify which objects are inside the affected
tablespace for the purposes of running your export, use the following query:

    select owner,segment_name,segment_type
    from dba_segments
    where tablespace_name='<name of tablespace>'

Now, export all the objects that you wish to keep.

Once the export is done, issue the DROP TABLESPACE tablespace INCLUDING
CONTENTS.  

Note that this PERMANENTLY removes all objects in this tablespace. Delete the
datafiles belonging to this tablespace using the operating system. (See the
comment above about possible problems in doing this.) Recreate the tablespace
with the datafile(s) desired, then import the objects into that tablespace.  
(This may have to be done at the table level, depending on how the tablespace
was organized.)  

NOTE:
The ALTER DATABASE DATAFILE <datafile name> OFFLINE DROP command, is not meant
to allow you to remove a datafile. What the command really means is that you
are offlining the datafile with the intention of dropping the tablespace.

If you are running in archivelog mode, you can also use:

    ALTER DATABASE DATAFILE <datafile name> OFFLINE;

instead of OFFLINE DROP.  Once the datafile is offline, Oracle no longer
attempts to access it, but it is still considered part of that tablespace. This
datafile is marked only as offline in the controlfile and there is no SCN
comparison done between the controlfile and the datafile during startup (This
also allows you to startup a database with a non-critical datafile missing).  
The entry for that datafile is not deleted from the controlfile to give us the
opportunity to recover that datafile.


If you do not wish to follow any of these procedures, there are other things
that can be done besides dropping the tablespace.

- If the reason you wanted to drop the file is because you mistakenly created
  the file of the wrong size, then consider using the RESIZE command.  

- If you really added the datafile by mistake, and Oracle has not yet allocated
  any space within this datafile, then you can use ALTER DATABASE DATAFILE
  <filename> RESIZE; command to make the file smaller than 5 Oracle blocks. If
  the datafile is resized to smaller than 5 oracle blocks, then it will never
  be considered for extent allocation. At some later date, the tablespace can
  be rebuilt to exclude the incorrect datafile.

leo_mei

sqlcode:

I adore you!!!!!!!!! and i have brought your anwner to FAQ.

parrotao

it is said by oracle.
you cant drop a  datafile from oracle
you can resize a datafile size down to 5M, oracle will igon this datafile.

史柯

可以：ALTER DATABASE DATAFILE ‘dele_file_path’OFFLINE DROP 即可

James Liu

Think of this way:

you have two data files, dbf1 and dbf2, for a tablespace called data01,
you have a table in data01 and the table is cross these two files, part of it in dbf1 and part of it in dbf2. What happens if you can drop one of the datafiles? Therefore, don't think you can drop a datafile. You can only drop a tablespace.

xduu

"At some later date, the tablespace can
be rebuilt to exclude the incorrect datafile."
oracle 会把5个datablock的datafile自动删除吗？

david31415

不会被自动删除吧？
我为了学习方便，
一直在tools tablespace里面加了几个size = 1M的datafile-

一直在呀？而且可以正确的操作-

能否在详细解释一下吗？