Help with db query and custom field in ot tax module

Hi, I have altered the ot_tax.php page and carried out an db query to check whether the vat exempt box was checked or not. If it was then the price should show without the vat, if it wasnt then the prices show with the vat.

Although I havent done the coding for the prices to show without vat. I just put an echo "you are vat exempt" just to see whether it worked or not. But all i get now is a blank page, no matter whether the checkbox is checked or not.

To be honest, I dont even know if I am editing the correct file or not.

But here is the code

<?php
/**
 * ot_tax order-total module
 *
 * @package orderTotal
 * @copyright Copyright 2003-2010 Zen Cart Development Team
 * @copyright Portions Copyright 2003 osCommerce
 * @license http://www.zen-cart.com/license/2_0.txt GNU Public License V2.0
 * @version $Id: ot_tax.php 17018 2010-07-27 07:25:41Z drbyte $
 */
 
 $dbhost = 'localhost';
$dbuser = 'myusername';
$dbpass = 'mypassword';

$conn = mysql_connect($dbhost, $dbuser, $dbpass) or die                      ('Error connecting to mysql');

$dbname = 'amobilit_zen';
mysql_select_db($dbname);

$query = mysql_query('SELECT customers_vatexemptconfirm FROM customers WHERE customers_vatexemptconfirm = "1"');

if ($query)
{

echo "You are VAT exempt";

} else {

  class ot_tax {
    var $title, $output;

    function ot_tax() {
      $this->code = 'ot_tax';
      $this->title = MODULE_ORDER_TOTAL_TAX_TITLE;
      $this->description = MODULE_ORDER_TOTAL_TAX_DESCRIPTION;
      $this->sort_order = MODULE_ORDER_TOTAL_TAX_SORT_ORDER;

      $this->output = array();
    }

    function process() {
      global $order, $currencies;

      reset($order->info['tax_groups']);
      $taxDescription = '';
      $taxValue = 0;
      if (STORE_TAX_DISPLAY_STATUS == 1)
      {
        $taxAddress = zen_get_tax_locations();
        $result = zen_get_all_tax_descriptions($taxAddress['country_id'], $taxAddress['zone_id']);
        if (count($result) > 0)
        {
          foreach ($result as $description)
          {
            if (!isset($order->info['tax_groups'][$description]))
            {
              $order->info['tax_groups'][$description] = 0;
            }
          }
        }
      }
      if (count($order->info['tax_groups']) > 1 && isset($order->info['tax_groups'][0])) unset($order->info['tax_groups'][0]);
      while (list($key, $value) = each($order->info['tax_groups'])) {
        if (SHOW_SPLIT_TAX_CHECKOUT == 'true')
        {
          if ($value > 0 or ($value == 0 && STORE_TAX_DISPLAY_STATUS == 1 )) {
            $this->output[] = array('title' => ((is_numeric($key) && $key == 0) ? TEXT_UNKNOWN_TAX_RATE :  $key) . ':',
                                    'text' => $currencies->format($value, true, $order->info['currency'], $order->info['currency_value']),
                                    'value' => $value);
          }
        } else
        {
          if ($value > 0 || ($value == 0 && STORE_TAX_DISPLAY_STATUS == 1))
          {
            $taxDescription .= ((is_numeric($key) && $key == 0) ? TEXT_UNKNOWN_TAX_RATE :  $key) . ' + ';
            $taxValue += $value;
          }
        }
      }
      if (SHOW_SPLIT_TAX_CHECKOUT != 'true' && ($taxValue > 0 or STORE_TAX_DISPLAY_STATUS == 1))
      {
        $this->output[] = array(
                        'title' => substr($taxDescription, 0 , strlen($taxDescription)-3) . ':' ,
                        'text' => $currencies->format($taxValue, true, $order->info['currency'], $order->info['currency_value']) ,
                        'value' => $taxValue);
      }
    }

    function check() {
	  global $db;
      if (!isset($this->_check)) {
        $check_query = $db->Execute("select configuration_value from " . TABLE_CONFIGURATION . " where configuration_key = 'MODULE_ORDER_TOTAL_TAX_STATUS'");
        $this->_check = $check_query->RecordCount();
      }

      return $this->_check;
    }

    function keys() {
      return array('MODULE_ORDER_TOTAL_TAX_STATUS', 'MODULE_ORDER_TOTAL_TAX_SORT_ORDER');
    }

    function install() {
	  global $db;
      $db->Execute("insert into " . TABLE_CONFIGURATION . " (configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, set_function, date_added) values ('This module is installed', 'MODULE_ORDER_TOTAL_TAX_STATUS', 'true', '', '6', '1','zen_cfg_select_option(array(\'true\'), ', now())");
      $db->Execute("insert into " . TABLE_CONFIGURATION . " (configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, date_added) values ('Sort Order', 'MODULE_ORDER_TOTAL_TAX_SORT_ORDER', '300', 'Sort order of display.', '6', '2', now())");
    }

    function remove() {
	  global $db;
      $db->Execute("delete from " . TABLE_CONFIGURATION . " where configuration_key in ('" . implode("', '", $this->keys()) . "')");
    }
  }
  
  
?>

Any help or giudance is much appreciated

No, you can't do that with a class, or well at least, if you do, you'll run into some dependency challenges.

It would be more in keeping with normal usage if you were to put your logic inside the process() method of the class, instead of your current approach which completely skips even the declaration of the class at all if your db query fails.

But even moreso, your query has no logic in it to identify which customer you're querying about in the first place.

I'd suggest it might be a lot more efficient if you used one of the already-built tax-exempt plugins instead.