SQL> select name from v$datafile;

NAME
--------------------------------------------------------------------------------

C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\SYSTEM01.DBF
C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\UNDOTBS01.DBF
C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\SYSAUX01.DBF
C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\USERS01.DBF
C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\EXAMPLE01.DBF


SQL> select a.TABLESPACE_NAME, round(total,1) Total_M, round(free) Free_M, round
(100*(1-free/total),1) Usage
  2  from (select TABLESPACE_NAME,sum(BYTES)/(1024*1024) total from dba_data_fil
es group by TABLESPACE_NAME) a
  3  ,(select TABLESPACE_NAME,sum(BYTES)/(1024*1024) free from dba_free_space gr
oup by TABLESPACE_NAME) b
  4  where a.TABLESPACE_NAME=b.TABLESPACE_NAME(+) order by 4 DESC;

TABLESPACE_NAME                   TOTAL_M     FREE_M      USAGE
------------------------------ ---------- ---------- ----------
SYSTEM                                490          5         99
USERS                                21.3          1       97.1
SYSAUX                                360         13       96.4
EXAMPLE                               100         23       77.4
UNDOTBS1                               30         18       41.7


SQL> create tablespace ts_saletarget datafile 'C:\ORACLE\PRODUCT\10.2.0\ORADATA\
ORCL\EXAMPLE01.DBF' size 15M;
create tablespace ts_saletarget datafile 'C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\
EXAMPLE01.DBF' size 15M
*
ERROR at line 1:
ORA-01537: cannot add file
'C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\EXAMPLE01.DBF' - file already part of
database


SQL> create tablespace ts_saletarget datafile 'C:\ORACLE\PRODUCT\10.2.0\ORADATA\
ORCL\EXAMPLE01.DBF' size 15M;
create tablespace ts_saletarget datafile 'C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\
EXAMPLE01.DBF' size 15M
*
ERROR at line 1:
ORA-01537: cannot add file
'C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\EXAMPLE01.DBF' - file already part of
database