SWITCH TO A NEW UNDO TABLESPACE AND DROP OLD UNDO TABLESPACE
sqlplus "/ as sysdba"
SQL> show parameter undo_tablespace
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
undo_tablespace string UNDOTBS1
SQL> create undo tablespace undo2
2 datafile 'c:\oracle\oradata\ORCL\undo2.dbf'
3 size 10m autoextend on ;
Tablespace created.
SQL> alter system set undo_tablespace=undo2 ;
System altered.
SQL> show parameter undo_tablespace
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
undo_tablespace string UNDO2
SQL> drop tablespace undotbs1 ;
Tablespace dropped.
SQL> create pfile from spfile ;
File created.
-- FOR WINDOWS INSTALLATION
SQL> shutdown immediate ;
Database closed.
Database dismounted.
ORACLE instance shut down.
-- DROP THE DATAFILE ASSOCIATED WITH THE
-- OLD UNDO TABLESPACE ON WINDOWS.
SQL> startup
ORACLE instance started.
....
Database opened.
SQL> show parameter undo_tablespace ;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
undo_tablespace string UNDO2