Changing Oracle Database characterset

Here is how to change the DB characterset

SELECT * FROM V$NLS_PARAMETERS WHERE PARAMETER LIKE '%CHARACTERSET%';

select * from V$nls_parameters where parameter in ('NLS_CHARACTERSET', 'NLS_NCHAR_CHARACTERSET');

or

select * from nls_database_parameters;

SHUTDOWN IMMEDIATE;

STARTUP RESTRICT;

ALTER DATABASE CHARACTER SET INTERNAL_USE AL32UTF8;

ALTER DATABASE CHARACTER SET AL32UTF8;

SHUTDOWN IMMEDIATE;

STARTUP;

SELECT * FROM V$NLS_PARAMETERS WHERE PARAMETER LIKE '%CHARACTERSET%';

For RAC

You need to stop the database. 

Start in single instance

alter system set cluster_database= false scope=spfile;

shut immediate;

startup restrict;

and follow above steps and change cluster_database=true once done and start db using srvctl normally

*********************************************************************

some times you might need to change ncharset of database.. follow steps below

Select property_value from database_properties
     where upper(property_name) = 'NLS_NCHAR_CHARACTERSET';

SHUTDOWN IMMEDIATE
STARTUP MOUNT
ALTER SYSTEM ENABLE RESTRICTED SESSION;
ALTER DATABASE OPEN;
ALTER DATABASE NATIONAL CHARACTER SET UTF8;
SHUTDOWN IMMEDIATE
STARTUP

It is always not better choice to use 'ALTER DATABASE' command to change the character set.

Make sure to take a full backup before doing this