Oracle Message ORA-01502 - index string.string or partition of such index is in unusable state

ERRORindex string.string or partition of such index is in unusable state
CAUSEAn attempt has been made to access an index or index partition that has been marked unusable by a direct load or by a DDL operation
ACTIONDROP the specified index, or REBUILD the specified index, or REBUILD the unusable index partition

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