PHP shopping cart and MySQL

Heather

Could someone please help me, I need to store the total amount from a php shopping cart in a database. It is already storing the session id, the item and the quantity ordered in a sales order table. Here is the code I'm using (I'm quite new to this):

my_shoppingcart.php
<?

if(!$session && !$ShoppingCart) //make sure this hasn't already been established
{
$session = md5(uniqid(rand())); //creates a random session value

// sets a cookie with the value of session.

// set the cookie to remain for 30 minutes
SetCookie( "ShoppingCart", "$session",time()+1800);
}
class Cart
{

function add_item($table,$session,$product,$quantity)
{
// Checks to see if they already have that product in their list
$in_list = "SELECT * FROM $table WHERE session='$session' ";
$in_list .= "AND product='$product'";
$result = mysql_query( "$in_list");
$num_rows = mysql_num_rows($result);

        // they don't have that product in their cart?  Put it in. 
       if($num_rows == 0)
       {
          $sql =  "INSERT INTO $table (session,product,quantity) VALUES ";
          $sql .=  "('$session','$product','$quantity')";
          mysql_query( "$sql");
       }
        // They have the product in their cart already?  Add the quantity they specified 
        // to the product they have in their cart 
       else
       {
          $row = mysql_fetch_array($result);
          $quantity = $quantity + $row[quantity];
          $sql =  "UPDATE $table SET quantity='$quantity' WHERE ";
          $sql .=  "session='$session' AND product='$product'";
          mysql_query( "$sql");
       }
    }
     // delete a specified item 
    function delete_item($table,$session,$product)
    {
       mysql_query( "DELETE FROM $table WHERE session='$session' AND product='$product'");
    }
     // modifies a quantity of an item 
    function modify_quantity($table, $session, $product, $quantity)
    {
       $sql =  "UPDATE $table SET quantity='$quantity' ";
       $sql .=  "WHERE session='$session' AND product='$product'";
       mysql_query( "$sql");
    }
     // clear all content in their cart 
    function clear_cart($table,$session)
    {
       mysql_query( "DELETE FROM $table WHERE session='$session'");
    }
     //add up the shopping cart total 
    function cart_total($table,$session)
    {
       $result = mysql_query( "SELECT * FROM $table WHERE session='$session'");
       if(mysql_num_rows($result) >0)
       {
          while($row = mysql_fetch_array($result))
          {
              // look up the item in inventory 
             $price_from_inventory =  "SELECT price FROM inventory WHERE ";
             $price_from_inventory .=  "product = '$row[product]'";
             $result_inventory = mysql_query( "$price_from_inventory");
             $row_price = mysql_fetch_array($result_inventory);
              //calculate the total 
             $total = $total + ($row_price[price]*$row[quantity]);
          }
       }
       return $total;
       }
     function display_contents($table,$session)
     {
     $count = 0;
     $result = mysql_query( "SELECT * FROM $table WHERE session='$session'");
     while($row = mysql_fetch_array($result))
     {
        $result_inv = mysql_query( "SELECT * FROM inventory WHERE product='$row[product]'");
        $row_inventory = mysql_fetch_array($result_inv);
        $contents[ "product"][$count] = $row_inventory[product];
        $contents[ "price"][$count] = $row_inventory[price];
        $contents[ "quantity"][$count] = $row[quantity];
        $contents[ "total"][$count] = ($row_inventory[price] * $row[quantity]);
        $count ++;
     }
      $total = $this->cart_total($table,$session);
      $contents[ "final"] = $total;
      return $contents;
     }
     function num_items($table, $session)
     {
        $result = mysql_query( "SELECT * FROM $table WHERE session='$session'");
        $num_rows = mysql_num_rows($result);
        return $num_rows;
     }
}

my_view_cart.php
<?
mysql_connect("localhost", "username", "password");
mysql_select_db( "test_db");
include( "my_shoppingcart.php");
$table = "sales_order";
$cart = new Cart;

if($add)
{
if($ShoppingCart)
$session = $ShoppingCart;

 $result = mysql_query(  "SELECT * FROM inventory WHERE product='$add'");
 $row = mysql_fetch_array($result);

 $cart->add_item($table,$session,$row[product],1);

}

if($remove)
{
if($ShoppingCart)
{
$session = $ShoppingCart;
}

 $result = mysql_query(  "SELECT * FROM inventory WHERE product='$remove'");
 $row = mysql_fetch_array($result);
 $cart->delete_item($table,$session,$row[product]);

}
if($modify)
{
$contents = $cart->display_contents($table,$session);
for($i = 0; $i < sizeof($quantity); $i++)
{
$oldquan = $contents[quantity][$i];
$product = $contents[product][$i];
$newquan = $quantity[$product];
$cart->modify_quantity($table,$session,$product,$newquan);
}
}
// End update cart

?>
<html>
<head>
<title>Shopping Cart</title>
<link rel="stylesheet" href="text_box.css" type="text/css">
<link rel="stylesheet" href="lotto.css" type="text/css">
</head>

<font size="6" face="Copperplate Gothic Bold"><CENTER>Shopping
Cart Items</font></td>
</center>
</TABLE>
<p><center><TABLE BORDER=1 cellpadding=2></center>
<TR>

<TD><font size="4" face="Copperplate Gothic Bold">Product</font></TD>
<TD><font size="4" face="Copperplate Gothic Bold">Price</font></TD>
<TD><font size="4" face="Copperplate Gothic Bold">Quantity</font></TD>
<TD><font size="4" face="Copperplate Gothic Bold">Total</font></TD>
<TD> </TD>

if($ShoppingCart)
{

$session = $ShoppingCart;
}

$contents = $cart->display_contents($table,$session);
if($contents[product][0] != "")
{
$x = 0;
while($x != $cart->num_items($table,$session))
{
echo "<TR><TD>".$contents[product][$x]. "</TD><TD>€".$contents[price][$x]. "</TD>\n";
$product = $contents[product][$x];
echo "<TD><INPUT TYPE=text size=3 name=quantity[$product] ";
echo "value=\"".$contents[quantity][$x]. "\"></TD>";
echo "<TD>€".$contents[total][$x]. "</TD>\n";
echo "<TD><A HREF=\"my_view_cart.php?remove=".urlencode($contents[product][$x]);
echo "".(!$ShoppingCart? "&session=$session": ""). "\">Remove</A>";
$x ++;

}
echo  "</TD><TR></TABLE>";
echo  "<BR><B><center>Total Order Amount: &euro;".$cart->cart_total($table,$session). "</center></B>";
echo  "<BR><center><INPUT TYPE=submit name=modify value=\"Recalculate Order\"></center>";
echo  "<BR><BR>";

}

else

echo "<p><center>There are no items in your shopping cart.</center>";
?>

</FORM>
</BODY>
</HTML>

I'm really stuck, please help!!