สอบถามเรื่องการ update หลาย rows ด้วย PK 2 ตัวครับ

$amt_arr = array(4,7);
foreach($amt_arr as $amt){
insert into tb_order ....
update tb_product set amount=amount-$amt where pro_id = 'รหัสสินค้า'
}

<?
require("inc/conndb.php");
$query_select  = "SELECT orders.*, products.* FROM orders JOIN products ON orders.p_id = products.p_id WHERE  (o_id LIKE '%".$keyword."%') ORDER BY o_id ASC";
$result_select  = mysql_query($query_select);

$rows = array();
while($row = mysql_fetch_array($result_select))
    $rows[] = $row;
foreach($rows as $row){ 
    $p_id= $row['p_id'];
	$o_amt= $row['o_amt');
    $o_date= $row['o_date'];
    $o_id= $row['o_id'];

    echo $o_id. '<br/>';
    echo $p_id. '<br/>';
    echo $o_amt. '<br/>';
    echo $o_date. '<br/><br/><br/><br/>';
}
?>

<form action="" method="post">
<input type="submit" name="update" value="update">
</form>

<?
if(isset($_POST['update'])){
$update = "UPDATE orders JOIN products ON orders.p_id = products.p_id SET p_amt = p_amt - $o_amt WHERE orders.o_id = '$o_id' AND products.p_id = '$p_id'";
mysql_query($update);
echo '<meta charset="utf-8">';
exit("<script>alert('อัพเดตเรียบร้อย');</script>");
}
?>

<?
require("inc/conndb.php");
$query_select = "SELECT orders.*, products.* FROM orders JOIN products ON orders.p_id = products.p_id WHERE (o_id LIKE '%".$keyword."%') ORDER BY o_id ASC";
$result_select = mysql_query($query_select);

$rows = array();
while($row = mysql_fetch_array($result_select))
$rows[] = $row;
foreach($rows as $row){ 
$p_id= $row['p_id'];
$o_amt= $row['o_amt');
$o_date= $row['o_date'];
$o_id= $row['o_id'];

echo $o_id. '<br/>';
echo $p_id. '<br/>';
echo $o_amt. '<br/>';
echo $o_date. '<br/><br/><br/><br/>';
}
?>

<form action="" method="post">
<input type="submit" name="update" value="update">
</form>

<?
if(isset($_POST['update'])){
foreach($rows as $row2){ 
$p_id2 = $row2['p_id'];
$o_amt2 = $row2['o_amt');
$o_date2 = $row2['o_date'];
$o_id2 = $row2['o_id'];
$update = "UPDATE orders JOIN products ON orders.p_id = products.p_id SET p_amt = p_amt - $o_amt2 WHERE orders.o_id = '$o_id2' AND products.p_id = '$p_id2'";
mysql_query($update);
}
echo '<meta charset="utf-8">';
exit("<script>alert('อัพเดตเรียบร้อย');</script>");
}
?>