select i, coalesce(lpad('*', count(s), '*'), ' ') from (             
  select trunc(salary, -3) s from 
    employees 
) stat right join 
   (select level*1000 i from dual connect by level <= 25) r
on r.i = stat.s
group by i
order by i

resultat:

1000	 
2000	************************
3000	******************
4000	*******
5000	*
6000	**********
7000	***********
8000	*********
9000	********
10000	******
11000	****
12000	***
13000	**
14000	*
15000	 
16000	 
17000	**
18000	 
19000	 
20000	 
21000	 
22000	 
23000	 
24000	*
25000