ORACLE表空间使用率

select a.tablespace_name,
       a.bytes bytes_used,
       b.free_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) free_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