mysql random pin generation function

gistfile1.txt

drop function if exists randalpha;

create function randalpha (s varchar(100))
returns char(1)
return substring(s, floor (rand() * length(s) + 1), 1);

drop function if exists randpin;

delimiter //
create function randpin(l int, r varchar(100))
returns varchar(100)
begin
  declare i int;
  declare pin varchar(100);
  set pin = '';
  set i = 1;
  while i <= l do
  set pin = concat(pin,randalpha(r));
  set i = i + 1;
  end while;
  return pin;
end//
delimiter ;