Cause
When you ALTER DATABASE ... CHARACTER SET, the new character set must be a superset of the old character set. For example, WE8ISO8859P1 is not a superset of the WE8DEC.
When you ALTER DATABASE ... CHARACTER SET, the new character set must be a superset of the old character set. For example, WE8ISO8859P1 is not a superset of the WE8DEC.
Specify a superset character set.
Try the following links for this error:
http://docs.oracle.com/cd/E16655_01/server.121/e26079/e12700.htm
https://community.oracle.com/message/1462841
https://community.oracle.com/message/4033661
https://community.oracle.com/message/1374232
https://community.oracle.com/message/2076431
https://community.oracle.com/message/9170381
https://community.oracle.com/message/9504806
https://community.oracle.com/message/9995429
https://community.oracle.com/message/10639073
https://community.oracle.com/message/4509915
https://community.oracle.com/message/4167236
https://community.oracle.com/message/10229511
https://community.oracle.com/message/2475372
https://community.oracle.com/message/1751126
https://community.oracle.com/message/1572613
https://community.oracle.com/message/10972706
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