mysql> select username, count(comments.id) as comments from users join comments on comments.userid = users.id group by users.id order by comments desc limit 10;
+------------------------------+----------+
| username | comments |
+------------------------------+----------+
| John_Brainlove | 7811 |
| fullerov | 5430 |
| wishpig | 4187 |
| Mike_Diver | 4070 |
| marcofella | 4047 |
| tom_from_sparks | 3758 |
| bamos | 3721 |
| shadyadie | 3645 |
| homesick_alien | 3597 |
| i-deserve-to-be-in-your-band | 3472 |
+------------------------------+----------+