查看用户和默认表空间的关系。      select   username,default_tablespace   from   dba_users;

1.查看表结构:desc表名

2.查看当前用户的表:

  1. select table_name from user_tables;  

3.查看所有用户的表名:

  1. select  table_name  from all_tables;  

4.查看所有表名(其中包括系统表)

  1. select table_name  from all_tables;    

5.查看所有的表:

  1. select *  from tab/dba_tables/dba_objects/cat;

下面介绍Oracle查询用户表空间

◆Oracle查询用户表空间:select * from user_all_tables

◆Oracle查询所有函数和储存过程:select * from user_source

◆Oracle查询所有用户:select * from all_users.select * from dba_users

◆Oracle查看当前用户连接:select * from v$Session

◆Oracle查看当前用户权限:select * from session_privs

◆Oracle查看用户表空间使用情况:

  1. select a.file_id “FileNo”,a.tablespace_name  

  2. “Tablespace_name”,  

  3. a.bytes “Bytes”,a.bytes-sum(nvl(b.bytes,0)) “Used”,  

  4. sum(nvl(b.bytes,0)) “Free”,  

  5. sum(nvl(b.bytes,0))/a.bytes*100 “%free”  

  6. from dba_data_files a, dba_free_space b  

  7. where a.file_id = b .file_id(+)  

  8. group by a.tablespace_name ,  

  9. a.file_id,a.bytes order by a.tablespace_name;

1.查看所有用户:    

select * from dba_user;    

select * from all_users;    

select * from user_users;  

2.查看用户系统权限:    

select * from dba_sys_privs;  

select * from all_sys_privs;    

select * from user_sys_privs;  

3.查看用户对象权限:    

select * from dba_tab_privs;    

select * from all_tab_privs;    

select * from user_tab_privs;  

4.查看所有角色:    

select * from dba_roles;  

5.查看用户所拥有的角色:    

select * from dba_role_privs;    

select * from user_role_privs;

6.查看角色所拥有的权限: 
  select * from role_sys_privs; 
  select * from role_tab_privs; 
7.查看所有系统权限 
  select * from system_privilege_map;  
8.查看所有对象权限 
  select * from table_privilege_map; 
以上是在Oracle中查看用户权限 ,  在DB2中为:    select * from syscat.dbauth    或者    get authorizations 
查看sid select * from v$instance