Oracle Error ORA-08111: a partitioned index may not be coalesced as a whole

Oracle Error Message

ORA-08111: a partitioned index may not be coalesced as a whole

Reason for the Error

User attempted to coalesce a partitioned index using ALTER INDEX COALESCE statement, which is illegal

Solution

Coalesce the index a (sub)partition at a time (using ALTER INDEX MODIFY (sub)PARTITION COALESCE)