SQL>select a.file#,a.name,c.tablespace_name,round(a.bytes//) CurrentMB,ceil(HWM*a.block_size)// ResizeTo,

(a.bytes-HWM*a.block_size)// ReleaseMB,'alter database datafile '||a.FILE#||' resize '||round(ceil(HWM*a.block_size)//+)||' M;' ResizeCmd

 from v$datafile a,(SELECT file_id,MAX(block_id+blocks-) HWM FROM DBA_EXTENTS GROUP BY file_id) b,dba_data_files c where a.file#=b.file_id(+)

 And (a.bytes-HWM*a.block_size)> and a.FILE#=c.file_id and c.tablespace_name not in('SYSTEM','SYSAUX') and c.tablespace_name not like'%UNDO%' order by  desc;

SQL> select group_number,name,total_mb/1024 TOTAL_GB,free_mb/1024 FREE_GB,free_mb/total_mb*100 free_percent,state,TYPE,(case when free_mb/total_mb*100 < 15 then '*' else '' end ) care from v$ASM_DISKGROUP;

SQL思路，查询每个数据文件中max_block_id *表空间的block_size，进行计算+5m（保守），是数据文件最大的大小，进行resize回收，排除undo,system,sysaux,temp表空间

查询数据库中大于2G的对象并列举出来， or ，将数据库中指定的users表空间，top 50对象列举出来

SQL> select * from (select owner,segment_name,segment_type,tablespace_name,round(sum(bytes)///,) "Gbytes" 

from dba_segments where bytes>** group by owner,segment_name,segment_type,tablespace_name) C1 where C1."Gbytes">;

or 

SQL> select rownum,C1.* from (select owner,segment_name,segment_type,tablespace_name,round(sum(bytes)/1024/1024/1024,2) "Gbytes"
 from dba_segments where bytes>1024*1024*50 and tablespace_name='USERS' group by owner,segment_name,segment_type,tablespace_name order by 4,5) C1 where rownum<50;