การเก็บข้อมูลเพิ่มจำนวนสินค้าจากสินค้าหลายๆตัวในฟอร์มเดียวกันลง DB

<?php
	$cat_id = $_GET[cat_id];
	if(empty($cat_id)){
		$cat_id = 1;
	}
	
	
	$sql_product 	= "select * from product where category_id ='$cat_id'"; 
	$product	= mysql_query($sql_product)or die(mysql_error());
	
    $sql_cat 	= "select * from category order by category_id";
	$cat	= mysql_query($sql_cat)or die(mysql_error());
?>


<form id="form1" name="form1" method="post" action="stockInSave.php"/>			
  <div class = category_list align="center">
	<tr>
      <th scope="row">Category</th>
      <td><select name="cat_name" onChange="MM_jumpMenu('parent',this,0)">
        
        
        
		<?php 
		$num_cat	= mysql_num_rows($cat);
		for($i=1;$i<=$num_cat;$i++)
		{
			$row_cat =	 mysql_fetch_array($cat);
		
		if($cat_id == $row_cat['category_id']){
			$sel = 'selected';
		}else{
			$sel = "";
		}
		
		?>
        
        <option value="stockIn0.php?cat_id=<?php echo $row_cat['category_id'] ?>" <?= $sel ?>><?php echo $row_cat['category_name'] ?></option>
        <?php
		}
		?>
      </select></td>
    </tr>
    </div> 
    
<table width="600" border="0" cellspacing="2">			
  <tr bgcolor="#BFCBFB">
    <td align="center"><strong>id</strong></td>
    <td align="center"><strong>image</strong></td>
    <td align="center"><strong>ชื่อสินค้า</strong></td>
    <td align="center"><strong>จำนวนคงเหลือ </strong></td>
    <td align="center"><strong>จำนวนสั่งเพิ่ม</strong></td>
  </tr>
  
  	<?php
		$num_pro = mysql_num_rows($product);
	
 		for ($i=1;$i<=$num_pro;$i++){
  			$row_pro = mysql_fetch_array($product);
	?>
  
	
  <tr>
    
    <td align="center"><?php echo $row_pro['product_id'] ?>&nbsp;</td>
    <td align="center"> 
    
	<img src="<?php echo "../".$row_pro['product_img'] ?>" width="100" />
    
    </td>
    <td><?php echo $row_pro['product_name'] ?>&nbsp;</td>
    <td align="center"><?php echo $row_pro['stock_now'] ?>&nbsp;</td>
    <td align="center"><input name="stock_in=<?php echo $row_pro['product_id'] ?>" type="text" id="stock_in" size="6" maxlength="6" /></td>
    
  <?php
	}
  ?>
  <tr>
	<th colspan="2" bgcolor="#FFCCCC" scope="row">

    <label><input type="submit" name="button1" id="button1" value="Update" /></label>
    <label><input type="reset" name="button2" id="button2" value="Reset" />  </label>

	</th>
  </tr>
</table>
</form>