dba_XXX 需要有許可權才能檢視，否則會報表和檢視不存在的錯誤

1. 查詢所有使用者(username, tablespace 資訊)

select * from dba_users;
select * from all_users;
//當前使用者
select * from user_users;  

2. 檢視使用者或角色的系統許可權

select * from dba_sys_privs;
//當前使用者擁有的許可權
select * from user_sys_privs;

3. 檢視當前登入使用者所擁有的角色所包含的許可權

select * from role_sys_privs;

select * from dba_tab_privs;
select * from all_tab_privs;   
select * from user_tab_privs;
 

5. 檢視所有角色

select * from dba_roles; 

6. 檢視使用者和角色所擁有的角色

select * from dba_role_privs;
select * from user_role_privs;

select * from v$PWFILE_USERS;

select * from dba_sys_privs where grantee='USERNAME';

select 'Drop table '||table_name||';' from all_tables where owner='USERNAME';
 

drop user USERNAME cascade;

select table_name from user_tables;

select 'truncate table '||tablename from user_tables;