{ { 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 }