ขอคำแนะนำเรื่องการออกรายงานตามข้อมูลจากวันที่ที่เราเลือกออกมาเป็น PDF คะ

<?php  
//export.php  
$conn = mysqli_connect("localhost", "root", "", "dbtest");
$conn->query("set names utf8");
$output = '';
if(isset($_POST["export"]))
{
 $query = "SELECT * FROM contact ";
 $result = mysqli_query($conn, $query);
 if(mysqli_num_rows($result) > 0)
 {
  $output .= '
   <table class="table" bordered="1">  
                    <tr>  
                         <th>ID</th>
                         <th>Name</th>  
                         <th>DEPARTMENT</th>  
                         <th>POINT</th>  
                         <th>CODE MACHINE</th>
                         <th>JOB ON</th>
                         <th>JOB NUMBER</th>  
                         <th>INV_CODE</th>  
                         <th>NAME PRODUCT</th>
                         <th>NUMBER</th>
                         <th>TIME</th>
                    </tr>
  ';
  while($row = mysqli_fetch_array($result))
  {
   $output .= '
                    <tr>  
                         <td>'.$row["idn"].'</td>  
                         <td>'.$row["name"].'</td>  
                         <td>'.$row["department"].'</td>  
                         <td>'.$row["point"].'</td>  
                         <td>'.$row["codemachine"].'</td>
                         <td>'.$row["job"].'</td>  
                         <td>'.$row["jobdate"].'</td>  
                         <td>'.$row["inv_code"].'</td>
                         <td>'.$row["name_product"].'</td>  
                         <td>'.$row["number"].'</td>  
                         <td>'.$row["time_hora"].'</td>
                    </tr>
   ';
  }
 }
}
{
 $query = "SELECT * FROM sensordata ";
 $result = mysqli_query($conn, $query);
 if(mysqli_num_rows($result) > 0)
 {
  $output .= '
   <table class="table" bordered="1">  
                    <tr>  
                         <th>SENSOR</th>
                         <th>LOCATION</th>  
                         <th>COUNT</th>  
                         <th>VAL</th>  
                         <th>CRACK</th>
                         <th>JOB NUMBER</th>
                         <th>TIME</th>  
                    </tr>
  ';
  while($row = mysqli_fetch_array($result))
  {
   $output .= '
                    <tr>  
                         <td>'.$row["sensor"].'</td>  
                         <td>'.$row["location"].'</td>  
                         <td>'.$row["value1"].'</td>  
                         <td>'.$row["value2"].'</td>  
                         <td>'.$row["value3"].'</td>
                         <td>'.$row["jobdate"].'</td>  
                         <td>'.$row["time_hora"].'</td>  

                    </tr>
   ';
  }
  $output .= '</table>';
  header('Content-Type: application/xls');
  header('Content-Disposition: attachment; filename=download.xls');
  echo $output;
 }
}
?>