Checking tablespace usage

SELECT tablespace_name                                     ||
       ' is '                                              ||
       TO_CHAR(ROUND(100-(free_bytes*100/total_bytes), 2)) ||
       '% full.' T, total_bytes, free_bytes
 FROM (SELECT a.tablespace_name, a.total_bytes, b.free_bytes
         FROM (SELECT tablespace_name,
                      NVL(SUM(bytes), 1) AS total_bytes
                 FROM dba_data_files
                GROUP BY tablespace_name) a,
              (SELECT tablespace_name, SUM(bytes) AS free_bytes
                 FROM dba_free_space
                GROUP BY tablespace_name) b
         WHERE a.tablespace_name = b.tablespace_name
      )
ORDER BY tablespace_name;

select a.TABLESPACE_NAME,
       a.BYTES bytes_used,
       b.BYTES bytes_free,
       b.largest,
       round(((a.BYTES-b.BYTES)/a.BYTES)*100,2) percent_used
  from
      (
        select TABLESPACE_NAME,
               sum(BYTES) BYTES
          from dba_data_files
         group by TABLESPACE_NAME
      ) a,
      (
        select TABLESPACE_NAME,
               sum(BYTES) BYTES ,
               max(BYTES) largest
          from dba_free_space
         group by TABLESPACE_NAME
      ) b
 where a.TABLESPACE_NAME=b.TABLESPACE_NAME
 order by ((a.BYTES-b.BYTES)/a.BYTES) desc