Determining how many datafiles make up a tablespace
To determine how many and which datafiles make up a tablespace, you can use the following query:

SELECT
file_name
, tablespace_name
FROM
dba_data_files
WHERE
tablespace_name ='<name of tablespace>';
Scenario 1
If the datafile you wish to remove is the only datafile in that tablespace, you can simply drop the entire tablespace using the following:

DROP TABLESPACE <tablespace name> INCLUDING CONTENTS;

Scenario 2
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;

Scenario 3

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 tablespace. Gather information on the current datafiles within the tablespace by running the following query in SQL*Plus:

SELECT
file_name
, tablespace_name
FROM
dba_data_files
WHERE
tablespace_name ='<name of tablespace>';