set session value after insert query - php

Question

I am trying to set a session variable after first successful insert query. I have a javascript Confirm to check if the user wants to add more data. If user wants to add more Products then I don't have to insert into the first table so keep the session value. If not then clear out the session data. I am not sure this is is right way of doing it. Could you please let me know if there are any suggestions.
<?php
if ($_SERVER['REQUEST_METHOD'] == 'POST')
{
session_start();
if (empty($_SESSION['new_id']))
{
$first = $_POST["first"];
$first = mysql_real_escape_string($first);
$last = $_POST["last"];
$last = mysql_real_escape_string($last);
$insertsql = "INSERT INTO Table1(FirstName,LastName) VALUES ('".$first."', '" .$last. "')";
$result1 = mysql_query($insertsql) or die(mysql_error());
$new_id = MySql_Insert_Id();
$_SESSION['new_id'] = $new_id;
}
$prodName = $_POST["prodName"];
$prodName = mysql_real_escape_string($prodName);
$prod_details = $_POST["prod_details"];
$prod_details = mysql_real_escape_string($prod_details);
$insertSQl2 = "INSERT INTO Table2($_SESSION['new_id'], Product_Name, Product_Details) VALUES ('".$new_id."', '" .$prodName. "', '" .$prod_details. "')";
$Result2 = mysql_query($insertSQl2) or die(mysql_error());
}
?>
<form>
//controls here
</form>
<?php
if($Result2 == true)
{
echo "Data saved Successfully";
echo '<script type="text/javascript">' , 'if confirm("Would like to add more Products?") ' , '</script>';
}
?>