Problem with getting data from mysql

I'm guessing you then do another query for that ID in the users table. That's how many forum databases work, anyway.

Using the ID allows for a generic representation (ie, ?user=48), and changing usernames. A user can update their name, or an administrator can, and all instances will be updated, as the ID is just a link to the name field in the users table for that individual user (specified by the ID).

How should this query look like?

SELECT username FROM phpbb_users .... and then???

Where ID = ...