Generate resize datafile script - oracle database script

SELECT 'alter database datafile'||' '''||file_name||''''||' resize '||round(highwater+2)||' '||'m'||';'
FROM
  (SELECT /*+ rule */ a.tablespace_name,
                      a.file_name,
                      a.bytes/1024/1024 file_size_MB,
                      (b.maximum+c.blocks-1)*d.db_block_size/1024/1024 highwater
   FROM dba_data_files a ,

     (SELECT file_id,
             max(block_id) maximum
      FROM dba_extents
      GROUP BY file_id) b,
        dba_extents c,

     (SELECT value db_block_size
      FROM v$parameter
      WHERE name='db_block_size') d
   WHERE a.file_id= b.file_id
     AND c.file_id = b.file_id
     AND c.block_id = b.maximum
   ORDER BY a.tablespace_name,
            a.file_name);