Oracle character set modification and related error handling

1. Under normal circumstances, use SQL> alter database CHARACTER SET ZHS16GBK; directly modify;

2. When the above command executes an error:
   ORA-12712: The new character set must be a superset of the old character set.

3. 1) Open sqlplus
   and log in as sysdba; conn sys/sys@orcl as sysdba;
   2) SHUTDOWN abort;
   3) STARTUP MOUNT;
   – ORA-12514: TNS: The listener currently does not recognize the connection description service requested in character
   - ORA-24324: uninitialized service handle
   　 - ORA-01041: internal error, hostdef extension does not exist
   　 When a refill error occurs:
   　 sql>quit;
   　 SQL> conn /as sysdba
   connected to idle routine .
   Then execute startup mount;
   4) SQL>ALTER SYSTEM ENABLE RESTRICTED SESSION;
   5) SQL>ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0;
   6) SQL>ALTER SYSTEM SET AQ_TM_PROCESSES=0;
   7) SQL>ALTER DATABASE OPEN;
   8) SQL>ALTER DATABASE CHARACTER SET INTERNAL_USE ZHS16GBK; //Skip supersubset detection
   9) SQL>SHUTDOWN IMMEDIATE;
   SQL>STARTUP