How to Change the NLS_CHARACTERSET

The syntax of the ALTER DATABASE CHARACTER SET statement is as follows:

ALTER DATABASE [db_name] CHARACTER SET new_character_set;

db_name is optional. The character set name should be specified without quotes. For example:

ALTER DATABASE CHARACTER SET AL32UTF8;

To change the database character set, perform the following steps:

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. Complete the following statements:

   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 new_character_set;
   SHUTDOWN IMMEDIATE; -- or SHUTDOWN NORMAL; 
   STARTUP;