Oracle DBA 简单操作
     --执行次数多的SQL
 select sql_text,executions from (
     select sql_text,executions from v$sqlarea order by executions desc
     ) where rownum<81;     
 --读硬盘多的SQL
 select sql_text,disk_reads from(
      select sql_text,disk_reads from v$sqlarea order by disk_reads desc
 )   where rownum<21;          
 --.查看所有用户:
 select * from dba_users;
 select * from all_users;
 select * from user_users;
 --查看用户或角色系统权限(直接赋值给用户或角色的系统权限):
 select * from dba_sys_privs;
 select * from user_sys_privs; 
 --查看角色(只能查看登陆用户拥有的角色)所包含的权限
 select * from role_sys_privs; 
 --查看用户对象权限
 select * from dba_tab_privs;
 select * from all_tab_privs;
 select * from user_tab_privs; 
 --查看所有角色
 select * from dba_roles; 
 --查看用户或角色所拥有的角色
 select * from dba_role_privs;  
 select * from user_role_privs; 
 --查看哪些用户有sysdba或sysoper系统权限(查询时需要相应权限)
 select * from V$PWFILE_USERS  
 SELECT name,spare4 FROM SYS.USER$ WHERE password is not null;