$query = qq(SELECT * FROM users WHERE userid = \'$username\');

$sth = $dbh->prepare($query);
$sth->execute;

$userCount = 0;
while (($userid, $pwd) = $sth->fetchrow_array) {
	print $userid . "is a valid user";
	$userCount = 1;
}


if($userCount == 0){
	print "invalid user";
}