    { { add_column_clause
      | modify_column_clause
      | drop_column_clause
      }
        [ add_column_clause
        | modify_column_clause
        | drop_column_clause
        ]...
    | rename_column_clause
    | modify_collection_retrieval
      [ modify_collection_retrieval ]...
    | modify_LOB_storage_clause
      [ modify_LOB_storage_clause ] ...
    | alter_varray_col_properties
      [ alter_varray_col_properties ] ...
    | REKEY encryption_spec
    }