oracle查询表空间使用情况

select 
b.file_id 文件ID, 
b.file_name 文件名,
b.tablespace_name 表空间名, 
b.bytes/1024/1024||\' M\' 字节数, 
(b.bytes-sum(nvl(a.bytes,0)))/1024/1024||\' M\' 已使用, 
sum(nvl(a.bytes,0))/1024/1024||\' M\' 剩余空间, 
trunc(100 - sum(nvl(a.bytes,0))/(b.bytes)*100,2) 占用百分比 
from dba_free_space a,dba_data_files b 
where a.file_id=b.file_id 
group by b.tablespace_name,b.file_id,b.bytes,b.file_name
order by b.file_id;

 查看表的空间大小：

select a.table_name,
    a.owner,
    a.tablespace_name,
    num_rows,
    b.bytes 
from dba_tables a,(select segment_name,sum(bytes)/1024/1024||\'M\' bytes from user_segments group by segment_name) b 
where a.table_name = b.segment_name
order by num_rows desc nulls last;