gistfile1.rb

  def generate_code
    chars = ("A".."Z").to_a + ("2".."9").to_a  # avoid ambiguity with 0/O and 1/I
    generated_code = ""
    1.upto(5) { |i| generated_code << chars[rand(chars.size - 1)] }

    return generated_code
  end

gistfile2.txt

mysql> SELECT code, COUNT(*) as cnt FROM leads GROUP BY code HAVING cnt > 1 ORDER BY cnt DESC;
+-------+-----+
| code  | cnt |
+-------+-----+
| 0YF2L |  36 | 
| RCTXQ |  17 | 
| OSYAG |  14 | 
| YF2LS |  10 | 
| CTXQB |   9 | 
| F2LSD |   6 | 
| R1T2U |   6 | 
| 2LSDZ |   6 | 
| ER1T2 |   5 | 
| 7JL0J |   5 | 
| 1T2UB |   4 | 
| TXQBM |   4 | 
| DZRER |   4 | 
| SYAG8 |   4 | 
| ZRER1 |   3 | 
| 01B27 |   3 | 
| 87JL0 |   3 | 
| D1BL6 |   3 | 
| 50CHJ |   3 | 
| YI77N |   3 | 
| QBMU5 |   3 | 
| 76YIK |   2 | 
| N1O75 |   2 | 
| WFRLE |   2 | 
| 3AQ01 |   2 | 
| YAG87 |   2 | 
| BBN50 |   2 | 
| YIK37 |   2 | 
| 43AQ0 |   2 | 
| RER1T |   2 | 
| 7OLUH |   2 | 
| L0JT4 |   2 | 
| CHJWN |   2 | 
+-------+-----+
33 rows in set (0.01 sec)