Экспорт отчета из sql

<?php 
  $file_name = 'report.txt';
  header("Content-Type: application/octet-stream");
  header("Content-Transfer-Encoding: Binary"); 
  header("Content-disposition: attachment; filename=\"" . basename($file_name) . "\""); 
?>
  <?php include_once("connection/data.php");?>

  $conn = new data();
       $sql = $conn->prepare("SELECT * FROM raspisanie, prepodovateli WHERE raspisanie.id_prepod=prepodovateli.id_prepod");
       $sql->execute(array());
      $report = "ID; ID секретный; Предмет; Группа; ID препод; Дата; ID формы обучения\n";


      while($rs = $sql->fetch()){
           $id = $rs['id'];
           $id_secret = $rs['$id_secret'];
           $predmet = $rs['predmet'];
           $groups = $rs['groups'];
           $id_prepod = $rs['id_prepod'];
           $dtr = $rs['dtr'];
           $id_form = $rs['id_form'];
           $report .= "$id, $id_secret, $predmet, $groups, $id_prepod ,$dtr , $id_form\n";
         }    

   $fp = fopen($file_name, "w");
   fwrite($fp, $report);
   fclose($fp);
   readfile($file_name);
?>