การเช็คและบวกเพิ่มจำนวนในตะกร้าสินค้าแบบ Session Array ในกรณีที่สินค้ากับออฟชั่นสินค้าตรงกับที่มีในตะกร้าสินค้าทำอย่างไรครับ

if(!isset($_SESSION['cart'][$id][$option])){  
$_SESSION['cart'][$id][$option][amount]+=$amount;
}else{
$sql="SELECT product.id AS id, product.name AS name, product.price AS price, product.image AS image, product_option.id AS option_id, product_option.name AS `option` FROM product, product_option WHERE product.id=$id AND product_option.id=$option";
$result=mysql_query($sql)or die(mysql_error());
$row=mysql_fetch_array($result);
$_SESSION['cart'][$id][$option]=array( 'name'=>$row['name'], 'image'=>$row['image'], 'price'=>$row['price'], 'option'=>$row['option']  ,'amount'=>$amount);
}

<?php 
if(!empty($_SESSION['cart'])){$cart=$_SESSION['cart'];
  if(sizeof($cart)>0){ 
?>
<form action="process/cart_update.php" method="post">
<table class="list" width="100%" border="0" align="center" cellpadding="5" cellspacing="1" bgcolor="#e5e5e5">
  <tr>
    <th width="40" align="center" bgcolor="#fafafa">ลบ</th>
    <th width="100" align="center" bgcolor="#fafafa">ภาพสินค้า</th>
    <th align="center" bgcolor="#fafafa">รายการสินค้า</th>
    <th width="65" align="center" bgcolor="#fafafa">ราคา</th>
    <th width="65" align="center" bgcolor="#fafafa">จำนวน</th>
    <th width="75" align="center" bgcolor="#fafafa">ราคารวม</th>
  </tr>
<? 
    $i=0; 
    $sum=0;
    $quantity=0;
    foreach($cart as $id=>$item){ 
?>
  <tr>
    <td align="center" bgcolor="#FFFFFF">
      <input class="form" type="checkbox" name="remove[]" value="<?=$id?>" />
    </td>
    <td align="center" bgcolor="#FFFFFF">
    <a href="product.php?product=<?php echo $item['id']?>" target="_blank"><img src="product/<?=$item['image']?>" width="90" border="0"/></a>
    </td>
    <td align="center" bgcolor="#FFFFFF"><?=$item['name']?><br/><?=$item['option']?></td>
    <td align="center" bgcolor="#FFFFFF"><?=number_format($item['price'])?></td>
    <td align="center" bgcolor="#FFFFFF">
      <a href="javascript:;"onclick="del('<?=$i+1?>')" style="display:block; margin-bottom:5px;"><img src="images/icon-minus.gif" border="0"/></a>
      <input class="form" style="width:20px; text-align:center;" name="amount[<?=$id?>]" type="text" id="<?=$i+1?>" value="<?=$item['amount']?>"/>
      <a href="javascript:;" onclick="plus('<?=$i+1?>')" style="display:block;margin-top:5px;"><img src="images/icon-plus.gif" border="0" /></a>
    </td>
    <td align="right" bgcolor="#FFFFFF"><?=number_format($item['price']*$item['amount'])?></td>
  </tr>
<? 	
    $sum+=$item['price']*$item['amount'];
    $quantity+=$item['amount'];
    $i++;
    }
?>
  <tr>
    <td colspan="5" align="right" style="background:#fafafa;">ราคารวม (บาท)</td>
    <td style="font-size:16px;background:#fafafa;" align="right"><?=number_format($sum)?></td>
  </tr>
</table>
</form>
<?php
  }
}
else{ 
?>
<div align="center" style="color:#999; font-size:13px;">
ไม่มีสินค้าในตะกร้า<br/>
<input name="button" type="button"  onclick="window.location='categories.php';" value="เลือกสินค้าต่อ" id="button_main"/></div>
<?php
} 
?>

<form action="process/cart_insert.php" method="post" >  
<span style="font-size:14px;">Color :</span>
<br />
<?
$sqlOption="SELECT * FROM product_option WHERE product_id=$_GET[product] AND name !='' ORDER BY id asc";
$resultOption=mysql_query($sqlOption)or die(mysql_error());
$numOption=mysql_num_rows($resultOption);
?>
<select name="option" style="width:200px; margin-top:3px;">
<?
for($i=1;$i<=$numOption;$i++){$rowOption=mysql_fetch_array($resultOption);
?>
<option value="<?=$rowOption['id']?>"><?=$rowOption['name']?></option>
<?
}
?>
</select>
<br />
<br />
<span style="font-size:14px;">Quantity :</span>
<div style="width:100px; text-align:center; margin-top:3px;">
<a href="javascript:;"onclick="del('<?=$i+1?>')" style="margin-bottom:5px;">
<img src="images/icon-minus.gif" border="0"/>
</a>
<input class="form" style="width:60px; text-align:center;" name="amount" type="text" id="<?=$i+1?>" value="1"/>
<a href="javascript:;" onclick="plus('<?=$i+1?>')" style="margin-top:5px;">
<img src="images/icon-plus.gif" border="0" />
</a>
</div>
<br />
<div id="main-price">
<div style="width:50px; float:left;">Price :</div>
<div style="width:400px; float:right; text-align:right;"><?=number_format($row['price'])?> ฿</div>
</div>
<input name="id" type="hidden" value="<?=$_GET['product']?>"/>
<input type="submit" value="เพิ่มลงตระกร้า / Add to Cart" id="cart_button"/>
</form>