สอบถามการใช้ GROUP BY หรือผิดตรงไหนครับ ช่วยดูให้หน่อยครับ

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<?
include "connection.php";
$chk = $_POST["chkorder"];
?>

<table width="700" border="0">
	  <tr>
		<th width="91"> <div align="center">Food_ID </div></th>
        <th width="91"> Food name </th>
		<th width="41"> <div align="center">Count</div></th>
        <th width="91"> <div align="center">sum price </div></th>
	  </tr>
  <?
for($j=0;$j<count($chk);$j++)
{
	if(trim($chk) != "")
	{
		echo "OrderID $j = '$chk[$j]'"; 
	}
?>       
<?
$sql="SELECT Food_ID,SUM(Qty) FROM orders_detail WHERE OrderID = '$chk[$j]' group by Food_ID";
$result = mysql_query($sql) or die(mysql_error($sql));
while($objResult = mysql_fetch_array($result))
{
 $foodID = $objResult['Food_ID'];
  $foodname = mysql_query("SELECT * FROM list_food WHERE Food_ID = '$foodID' ");
  while($objResult1 = mysql_fetch_array($foodname))
  	{ 
	
	for($i=0;$i<=1;$i++)
		 {
		$qty = $objResult['SUM(Qty)'];
		$price = $objResult1['price'];
		$t_price = $qty * $price;
		$tt_price = $qty[$i] * $price;
		$SumTotal = $SumTotal + $tt_price;
		 }
?>
	 <tr>
        <td align="center"><?=$objResult["Food_ID"];?></td>    
        <td><?=$objResult1["Food_Name"];?></td>
		<td align="center"><?=$objResult["SUM(Qty)"];?></td>
        <td align="center"><?=number_format($t_price,2);?></td>
	
    </tr>
<?
	}
}}
?>


            <p>
			    <tr> <td></td><td></td><td>รวมทั้งสิ้น</td>                              
              <td align="center"><?=number_format($SumTotal,2);?></td> <td>บาท</td>          
   </tr>  </table>      
<?
mysql_close();
?>