While changing character-set from AL32UTF8 to WE8MSWIN1252 got  "ORA-12712: new character set must be a superset of old character set".

Below are steps taken to resolve the issue -

ALTER DATABASE CHARACTER SET WE8MSWIN1252;

i got this error: ORA-12712: new character set must be a superset of old character set

After some googling I found solution, below are the commands executed by me:

SQL> SHUTDOWN IMMEDIATE;
SQL> CONNECT SYS/password AS SYSDBA;
SQL> STARTUP MOUNT;
SQL> ALTER SYSTEM ENABLE RESTRICTED SESSION;
SQL> ALTER DATABASE OPEN;
SQL> ALTER DATABASE CHARACTER SET INTERNAL_USE WE8MSWIN1252;
SQL> SHUTDOWN;
SQL> STARTUP;
SQL> QUIT;

And its working...