Cause
An attempt was made to use the DROP CONSTRAINT ONLINE or SET UNUSED COLUMN ONLINE statement on a constraint type other than check, primary key, unique, referential, or not null constraint.
An attempt was made to use the DROP CONSTRAINT ONLINE or SET UNUSED COLUMN ONLINE statement on a constraint type other than check, primary key, unique, referential, or not null constraint.
Submit the DROP INDEX <index> statement to drop the index.
Try the following links for this error:
http://docs.oracle.com/cd/E16655_01/server.121/e26079/e12700.htm
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