A better approach 

 comment_id | parent | score |                  text
------------+--------+-------+----------------------------------------
          4 |        |    19 | Top comment
          8 |      4 |    22 |     Top reply to top comment
         11 |      8 |    12 |         Top response to top reply
          9 |      8 |     1 |         Meh response to top reply
          5 |      4 |     6 |     Earliest reply to top comment
          7 |        |     3 | Less highly rated comment
         10 |      7 |     5 |     Reply to less highly rated comment
          3 |        |     0 | Crap comment that nobody wants to read