–查看用户和默认表空间的关系
select username,default_tablespace from dba_users;
–查看当前用户能访问的表
select * from user_tables; 
–Oracle查询用户表
select * from user_all_tables;

–Oracle查询用户视图
select * from user_views;
–查询所有函数和储存过程：
select * from user_source;
–查询所有用户：
select * from all_users;
–select * from dba_users
–查看当前用户连接：
select * from v$Session;
–查看用户角色
SELECT * FROM USER_ROLE_PRIVS;
–查看当前用户权限：
select * from session_privs;
–查看所有用户所拥有的角色
SELECT * FROM DBA_ROLE_PRIVS;
–查看所有角色
select * from dba_roles;
–查看数据库名
SELECT NAME FROM V$DATABASE;
–查看所有表空间使用情况
select a.file_id “FileNo”,
       a.tablespace_name “Tablespace_name”,
       a.bytes “Bytes”,
       a.bytes – sum(nvl(b.bytes, 0)) “Used”,
       sum(nvl(b.bytes, 0)) “Free”,
       sum(nvl(b.bytes, 0)) / a.bytes * 100 “%free”
  from dba_data_files a, dba_free_space b
 where a.file_id = b.file_id(+)
 group by a.tablespace_name, a.file_id, a.bytes
 order by a.tablespace_name;