Oracle: Resize Datafiles

with query as (
    select /*+ NO_MERGE MATERIALIZE */
        file_id,
        tablespace_name,
        max(block_id + blocks) highblock
    from
        dba_extents
    group by
        file_id, tablespace_name
)
select
    'alter database datafile '|| q.file_id || ' resize ' || ceil ((q.highblock * t.block_size + t.block_size)/1024)  || 'K;' cmd
from
    query q,
    dba_tablespaces t
where
    q.tablespace_name = t.tablespace_name;