How to get username from userid

[MikesSite]

I'm creating a php page for the forum that will show everybody from a specific string they input under the Additional Information / Details section. It's 'field2' located in the 'userfield' section of the forum database. Basically I am able to get the field2 string and userid, but I'm wondering how I can get the username from the userid?

if ($row['field2']=="United States") {
echo "<b>" . $row['userid'] . "</b> - <u>" . $row['field2'] . "</u>";
}

Thanks.

[vbplusme]

Assuming you are selecting user.username in your query $row['username']

Am I missing something?

[MikesSite]

selecting by userfield, there is no username row

mysql_select_db("forum") or die(mysql_error());
$b="SELECT * FROM userfield ORDER BY userid ASC";