problema con semplice pagina di login

[mr.click]

function auth_user($userid, $userpassword){
    global $default_dbname, $user_table;
    $link_id = db_connect();
    
    
    $query = "SELECT username FROM user WHERE userid = '$userid' AND userpassword= '$userpassword'";
    //echo $query;
    $result = mysql_query($query);     
    $row = mysql_fetch_array($result);
    echo $row['username'];
    //echo $result[0]."
";
    echo "...";
    $query_data = mysql_fetch_row($result);
    //echo $query_data[0];
    return $query_data[0]; 

prova cosi