Oracle获取当前用户

Function get_user return varchar2
is
   v_user    varchar2(30);
begin
   select sys_context('user_policy_context','uid')
    into v_user
    from dual_user ;
   if v_user is null then
      select user into v_user from dual_user;
   end if;
   return upper(v_user);
end get_user ;

set的方法:
dbms_session.set_context('user_policy_context','uid',uid);