count          character
    -------       ----------
     1               a
     2               s
     2               h
     1               i
     2               s
     2               h

  
       2            s
       2            s
       2            h
       2            h

declare
 v_str varchar2(1000);
  v_chr varchar2:='a'
   v_cnt number:=0;
begin
 v_str:='&name';
  for i in 1..length(v_str)
   loop
    if v_chr=substr(v_str, i, 1) then
      v_cnt:=v_cnt+1;
    end if;
   end loop;
 dbms_output.put_line('No of:'||v_chr||':'||v_cnt);
end;
/

declare
 v_str varchar2(1000) := '&name';
 v_chr varchar2(1);
 v_cnt number:=0;
begin
    for i in 1..length(v_str) loop
          v_chr := substr(v_str,i,1);
          v_cnt := 0;
      for j in 1..length(v_str) loop
          if v_chr = substr(v_str, j, 1) then
              v_cnt:=v_cnt+1;
          end if;  
      end loop;
      if instr ( substr(v_str,1,i-1),v_chr) = 0 or i = 1 then
          dbms_output.put_line('No of:'||v_chr||':'||v_cnt);
      end if; 
    end loop;
end;