1）查看dba用户

select * from V$PWFILE_USERS;      

2）查看oracle版本以及系统版本
   select * from v$version;                

3）查看当前用户拥有的权限值 DBA
select * from session_privs;         

4）查询当前用户角色

select * from user_role_privs          

5）查询当前用户系统权限

select * from user_sys_privs          

6）查看所有用户密码hash

select username,password from dba_users;

7）查系统权限

select * from dba_sys_privs where grantee='SYSTEM';

8）登陆不上OEM时候需要此权限

grant select any dictionary to system with admin option;

9）低版本查看单用户密码

Select name,password FROM user$ Where name='SCOTT';

10）查看用户hash

 Select username,decode(password,NULL,'NULL',password) password FROM dba_users;                                

11）建用户bob密码iloveyou

create user bob identified by iloveyou;

12）赋予bob DBA权限

grant dba to bob;                       

13）赋予用户execute

grant execute on xmldom to bob;        

14）当提示role 'JAVASYSPRIV' does not exist使用

    Create ROLE "javasyspriv" NOT IDENTIFIED

15）检查那些用户有DBA权限

select grantee from dba_role_privs where granted_role='DBA';

16）查看路径所在目录

select * from dba_directories;        

17）创建表空间

   create tablespace risenet
  2  datafile 'C:\ORACLE\ORADATA\TEST\risenet.dbf'
  3* size 400M;                         

18）更改用户的默认表空间

alter user risenet default tablespace risenet;

19）查看表是否在该默认的表空间

select table_name,tablespace_name from user_tables;

20)查看用户的连接的session

select sid,serial#,username from v$session;

21)数据库打开并在只读状态，只能查询，不能增、删、改，一般在维护时用

alter database open read only;

22)改为归档模式

alter database archivelog;

     SQL>archive log list;

23)查看表空间的创建语句

      SELECT DBMS_METADATA.GET_DDL('TABLESPACE', TS.tablespace_name) 
FROM DBA_TABLESPACES TS;