กดค้นหาแล้วค่า sum ไม่เลือกออกมา.....มันไม่ส่งค่ามาถึงตัวที่จะ sum ออกมาอ่ะคับ ผมผิดตงไหนครับ

<?php 
				 $tx = "";
				 if($_GET['work_year_id']!= "")
{
$tx .= "and ( work_year_id = '$_GET[work_year_id]' )";	
}
if($_GET['txtsearch']!= "")
{
$tx .= "and ( work_year_id like '%$_GET[txtsearch]%'  )";	
}
	  $i=1;
$str="select * from work_durable_2 where 1 $tx order by id desc";
$rs=mysql_query($str);
while($arr=mysql_fetch_array($rs)){
$str_n="SELECT * FROM tag_work_durable WHERE id='$arr[id]' ";
$rs_n=mysql_query($str_n);
$num_s=mysql_num_rows($rs_n);
$strSQL2 = "select * from work_durable_2 where work_year_id  $tx order by id desc ";
?>
      <tbody>
        <tr>
        <td align="center" width="50"><?php echo $i; ?></td>
          <td><a href="system_index_details_durable.php?id=<?php echo $arr['id']; ?>" target="_blank" ><u><?php echo $arr['work_duname']; ?></u></a></td>
          <td align="center" width="150"><?php if($num_s=="0"){  echo "0"; }else{ echo $num_s; } ?></td>
          <td align="right" width="150"><?php echo number_format($arr['work_day4price'],0); ?></td>
         
        </tr>
      </tbody>
         <?php
	$i++; }
	?>
    <?php $id = $_GET['id'];
	 $sql = "select sum(work_day4price) from work_durable_2 where work_year_id ='$_GET[work_year_id]' ";
	   $result = mysql_query($sql) or die ("error = $sql");
	    while ( $row = mysql_fetch_array($result))
		  {
	?>
      <tfoot>
                                    <tr>
                                        <th></th>
                                        <th><i>รวมงบลงทุนครุภัณฑ์</i></th>
                                        <th></th>
                                        <th><i><?PHP echo $row['work_day4price']; ?></i></th>
                                    </tr>
                                    </tfoot>
       <?php
		  }
		  ?>
    </table>