select t.teller
,      sum(decode(sign(teller - trunc(last_call_et/60/60)),'0',1,0)) aantal
,      rpad('*',sum(decode(sign(teller - trunc(last_call_et/60/60)),'0',1,0))/5,'*') leuke_sterretjes
from v$session
,    (select rownum-1 teller
      from dba_objects
      where rownum <= (select trunc(max(last_call_et/60/60))+1
                         from v$session where username is not null)
     ) t
where username is not null
and machine like 'bbapp%'
group by t.teller order by 1,2;