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);