Script for changing encoding of database

 (from http://aqeelabbasdba.blogspot.com/2012/12/how-to-change-oracle-database-chracter.html)

1. Shut down the database, using either a SHUTDOWN IMMEDIATE or a SHUTDOWN NORMAL statement.

2. Do a full backup of the database because the ALTER DATABASE CHARACTER SET statement cannot be rolled back.

3. Startup Oracle database

 startup mount;
 ALTER SYSTEM ENABLE RESTRICTED SESSION;
 ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0;
 ALTER SYSTEM SET AQ_TM_PROCESSES=0;
 ALTER DATABASE OPEN;
 ALTER DATABASE CHARACTER SET AL32UTF8;
If you get the error ORA-12712, please update the following table.

"ORA-12712: new character set must be a superset of old character set"

 update sys.props$ set VALUE$='AL32UTF8' where NAME='NLS_CHARACTERSET';
 commit;
If you get the error ORA-12721, please login as DBA user.

"ORA-12721: operation cannot execute when other sessions are active"

4. shutdown immediate;  or shutdown normal;

5. startup oracle database

 startup mount;
 ALTER SYSTEM ENABLE RESTRICTED SESSION;
 ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0;
 ALTER SYSTEM SET AQ_TM_PROCESSES=0;
 ALTER DATABASE OPEN;
 ALTER DATABASE CHARACTER SET AL32UTF8;

 shutdown immediate;
 startup;

--------------------------------------Check the NLS parameters-------------------------------------------
 SELECT PARAMETER, VALUE FROM NLS_DATABASE_PARAMETERS WHERE PARAMETER IN ('NLS_CHARACTERSET', 'NLS_NCHAR_CHARACTERSET');