方法1：
select a.tablespace_name,b.space "SUM SPACE",a.space "FREE SPACE",a.space/b.space "FREE percent"
from
(select sum(bytes)/1024/1024/1024 space,tablespace_name from dba_free_space group by tablespace_name) a,
(select sum(bytes)/1024/1024/1024 space,tablespace_name from dba_data_files group by tablespace_name) b
where a.tablespace_name=b.tablespace_name
方法2：
select a.tablespace_name, b.space "SUM GB",a.space "USED GB",b.space-a.space "FREE GB",(b.space-a.space)/b.space "FREE PERCENT"
from
(select sum(bytes)/1024/1024/1024 space,tablespace_name from dba_segments group by tablespace_name) a,
(select sum(bytes)/1024/1024/1024 space,tablespace_name from dba_data_files group by tablespace_name) b
where a.tablespace_name=b.tablespace_name
方法1的更准确
