get datafile currentSize/smallestSize/size can reduced

select file_name,
       ceil((nvl(hwm, 1) * &blocksize) / 1024 / 1024) smallest,
       ceil(blocks * &blocksize / 1024 / 1024) currsize,
       ceil(blocks * &blocksize / 1024 / 1024) - ceil((nvl(hwm, 1) * &blocksize) / 1024 / 1024) savings
  from dba_data_files a,
       (select file_id, max(block_id + blocks - 1) hwm
          from dba_extents
         group by file_id) b
 where a.file_id = b.file_id(+)