I got the procedure to change. But its giving the following error:

ORA-12712: new character set has to be a superset of old character set.

I am executing the following commands -

SQL> STARTUP MOUNT;
SQL> ALTER SYSTEM ENABLE RESTRICED SESSION;
SQL> ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0;
SQL> ALTER DATABASE OPEN;

SQL>alter database set characterset WE8ISO8859P15;

error
ORA-12712: new character set has to be a superset of old character set.


My old characterset is WE8ISO8859P1

obviously the new is a superset of the old. Why am I getting this error??