1、查看表空间的名称及大小  
select t.tablespace_name, round(sum(bytes/(1024*1024)),0) ts_size  
from dba_tablespaces t, dba_data_files d  
where t.tablespace_name = d.tablespace_name  
group by t.tablespace_name;  

2、查看表空间物理文件的名称及大小  
select tablespace_name, file_id, file_name,  
round(bytes/(1024*1024),0) total_space  
from dba_data_files  
order by tablespace_name;  

3、查看回滚段名称及大小  
select segment_name, tablespace_name, r.status,  
(initial_extent/1024) InitialExtent,(next_extent/1024) NextExtent,  
max_extents, v.curext CurExtent  
From dba_rollback_segs r, v$rollstat v  
Where r.segment_id = v.usn(+)  
order by segment_name ;  

4、查看控制文件  
select name from v$controlfile;  

5、查看日志文件  
select member from v$logfile;  

6、查看表空间的使用情况  
select sum(bytes)/(1024*1024) as free_space,tablespace_name  
from dba_free_space  
group by tablespace_name;  
SELECT A.TABLESPACE_NAME,A.BYTES TOTAL,B.BYTES USED, C.BYTES FREE,  
(B.BYTES*100)/A.BYTES "% USED",(C.BYTES*100)/A.BYTES "% FREE"  
FROM SYS.SM$TS_AVAIL A,SYS.SM$TS_USED B,SYS.SM$TS_FREE C  
WHERE A.TABLESPACE_NAME=B.TABLESPACE_NAME AND A.TABLESPACE_NAME=C.TABLESPACE_NAME;  

7、查看数据库库对象  
select owner, object_type, status, count(*) count# from all_objects group by owner, object_type, status;  

8、查看数据库的版本　  
Select version FROM Product_component_version  
Where SUBSTR(PRODUCT,1,6)='Oracle';  

9、查看数据库的创建日期和归档方式  
Select Created, Log_Mode, Log_Mode From V$Database;

10.
SQL> select name from v$database;

NAME
---------
ORACLE

11.
select * from v$instance
查询实例

12.select * from GLOBAL_NAME;