How to best generate a unique alphanumeric key

Question

Hi:
  I have a requirement to generate a unique alphanumeric key 20 characters long.
  I know that I can use sys.dbms_random.string('X', 20) but I also have a requirement to not include certain characters that could be missread, i.e. no 0 (zero), O(uppercase oh) and a few others.
  My questions are:
     1) Is there a way to tell dbms_random to not include certain characters in the key generation
     2) If the answer to 1 is No, what would be the best way to replace the unwanted characters.  I am thinking just do a translate right afterwards with a randomly generated set of characters that do not include the characters I am interested in and seeded
         upon package initialization.  Any other ideas.
    3) Is there a better way of meeting this requirement within PL/SQL?
Thanks,
Thomas

Answer 1

The most safe would be to use something like below if efficient enough
select listagg(x.ltr,'') within group (order by y.step desc) key
  from (select level lvl,
               substr(:alphabet,level,1) ltr
          from dual
        connect by level <= length(:alphabet)
       ) x,
       (with
        to_base(step,num,base,quot,remain) as
        (select 1 step,num,base,trunc(num / base) quot,mod(num,base) remain
           from (select :sequence_value num,length(:alphabet) base
                   from dual
                  where :sequence_value between power(length(:alphabet),:key_length - 1)
                                            and power(length(:alphabet),:key_length) - 1
         union all
         select step + 1,quot,base,trunc(quot / base),mod(quot,base)
           from to_base
          where num > 0
        select step,remain
          from to_base
         where num > 0
       ) y
where x.lvl = y.remain + 1
Regards
Etbin