SQL>conn / as sysdba


SQL> select * from nls_database_parameters where parameter='NLS_CHARACTERSET';


PARAMETER
------------------------------
VALUE
--------------------------------------------------------------------------------
NLS_CHARACTERSET
AL32UTF8




SQL> shu immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.


Total System Global Area 6.2934E+10 bytes
Fixed Size    2268712 bytes
Variable Size 6039798232 bytes
Database Buffers 5.6774E+10 bytes
Redo Buffers  118157312 bytes
Database mounted.
SQL> alter system enable restricted session;


System altered.


SQL> alter database open;


Database altered.


SQL> alter database character set ZHS16GBK;
alter database character set ZHS16GBK
*
ERROR at line 1:
ORA-12712: new character set must be a superset of old character set




SQL> alter database character set internal_use ZHS16GBK;


Database altered.


SQL> shu immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.


Total System Global Area 6.2934E+10 bytes
Fixed Size    2268712 bytes
Variable Size 6039798232 bytes
Database Buffers 5.6774E+10 bytes
Redo Buffers  118157312 bytes
Database mounted.
Database opened.
SQL> select * from nls_database_parameters where parameter='NLS_CHARACTERSET';


PARAMETER
------------------------------
VALUE
--------------------------------------------------------------------------------
NLS_CHARACTERSET
ZHS16GBK