select * from dba_users; see inside the database for all users, provided you have dba privileges of the account, such as SYS, System
the SELECT * from all_users; you can see all the users manage!
select * from user_users; view current user information!
- under your current user query, which tables
the SELECT * the FROM USER_TABLES
- under your current user queries, which can be accessed tables [that is, access to their own and other users of]
the SELECT * the FROM all_tables
- query the current database of all the tables, you need to have DBA privileges
SELECT * FROM dba_tables