计算表空间可以收缩的大小

 1 select a.file#,a.name,a.bytes/1024/1024 CurrentMB,
 2      ceil(HWM * a.block_size)/1024/1024 ResizeTo,
 3        (a.bytes - HWM * a.block_size)/1024/1024 ReleaseMB,
 4        'alter database datafile '''||a.name||''' resize '||
 5        ceil(HWM * a.block_size/1024/1024) || 'M;' ResizeCMD
 6 from v$datafile a,
 7      (select file_id,max(block_id+blocks-1) HWM
 8        from dba_extents e 
 9        where exists(select 1 From dba_data_files
10                              where tablespace_name='LMPS_USERS_201307' and file_id=e.file_id)
11        group by file_id) b
12 where a.file# = b.file_id(+)
13 and (a.bytes - HWM *block_size)>0
14 order by 5