Cause
An attempt was made to DROP or SET UNUSED a column that has already been 'set unused'.
An attempt was made to DROP or SET UNUSED a column that has already been 'set unused'.
Use the DROP UNUSED COLUMNS option to remove the column.
Try the following links for this error:
http://docs.oracle.com/cd/E16655_01/server.121/e26079/e12700.htm
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