问如何检查撤消表空间的当前大小？

EN

select t1.tablespace_name "Tablespace name"
       , total_used_space "Used MB"
       , (t1.total_space - t2.total_used_space) "Free MB"
       , t1.total_space "Total MB"
       , round(100 * ( (t1.total_space - t2.total_used_space)/ t1.total_space))
"Percentage Free"
from (select tablespace_name
             , round(sum(bytes) / 1048576) Total_Space
      from dba_data_files
      group by tablespace_name) t1,
     (select round(sum(bytes)/(1024*1024)) total_used_space
             , tablespace_name
      from dba_segments
      group by tablespace_name) t2
      where t1.tablespace_name = t2.tablespace_name ;