PHP error "Call to a member function query_column"

Here is the code, i am trying to make it so when someone does a / then a name the error php actually looks at this script and i am going to save whatever they put as / name as a session variable.  I run the script and i get the error

Fatal error: Call to a member function query_column() on a non-object in /home/maxgxl/public_html/replicate.php on line 28

I marked line 28 in the code

<?PHP
session_start();

$username_lookup = rtrim($_SERVER['REDIRECT_URL'],'/');
preg_match('/\/[A-Za-z0-9_\- ]+$/', $_SERVER['REDIRECT_URL'], $matches);
$username_lookup = substr(trim($matches[0]),1);

if($username_lookup){
      
      
      $ho = '';      
   $us = '';
   $pa = '';
   $dbName = '';

   // connect and select the database
   $conn = mysql_connect($ho, $us, $pa) or die(mysql_error());
   $db = mysql_select_db($dbName, $conn) or die(mysql_error());
      unset($_SESSION["user"]);

      
      28.   if($db->query_column("select user2 from username2 where user2='" . $username_lookup . "'")){
            $_SESSION["user"]["username"] = strtolower($username_lookup);
      }else{
            if($db->query_column("select user2 from distributors where username='" . $username_lookup . "' and active=1")){
                  $_SESSION["user"]["username"] = strtolower($username_lookup);
            }      
      }
      
      if($username_lookup == 'clearsession'){
            unset($_SESSION["user"]);
      }
}

if(!$_SESSION["user"]["username"]){
      header("Location: /real404.php");
}else{
      //header("Location: /index.php");
      include('index.php');
}

echo "<!--" . @$_SESSION["user"]["username"] . "-->";
?>


Looking for any advice on the coding.
Start Free Trial