Thank you all for the replies!
On Wed, Mar 9, 2011 at 7:01 PM, David Johnston <polobo(at)yahoo(dot)com> wrote:
> SELECT username, count(username) FROM phpbb_users
> GROUP BY username
> HAVING count(username) > 1;
>
> If anything shows up then (phpbb_users .username) is not a unique field but
> you are trying to insert it into one that is (drupal_users.uid)
>