更改oracle字符集 error: ora-12712 解决方法

sqlplus log
conn /as sysdba
shutdown immediate;
startup mount;
ALTER SESSION SET SQL_TRACE=TRUE;
ALTER SYSTEM ENABLE RESTRICTED SESSION;
ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0;
ALTER SYSTEM SET AQ_TM_PROCESSES=0;
ALTER DATABASE OPEN;
set linesize 120;
alter database character set zhs16gbk;

RROR at line 1:
　　ORA-12712: new character set must be a superset of old character set

ALTER DATABASE character set INTERNAL_USE zhs16gbk;
ALTER SESSION SET SQL_TRACE=FALSE;
shutdown immediate;
STARTUP
select NLS_CHARACTERSET from nls_database_parameters;