However it sounds like you are saying when a second order is placed, it is overwriting the first.
This can happen if you place a second order using the same browsing session, which is not likely for your customers to do. you can add the following code to destroy the session on the checkout success page after the closing </html> tag to prevent this unlikely in the real world issue:
<?php
// Initialize the session.
// If you are using session_name("something"), don't forget it now!
@session_start();
// Unset all of the session variables.
$_SESSION = array();
// If it's desired to kill the session, also delete the session cookie.
// Note: This will destroy the session, and not just the session data!
if (ini_get("session.use_cookies")) {
$params = session_get_cookie_params();
@setcookie(session_name(), '', time() - 42000,
$params["path"], $params["domain"],
$params["secure"], $params["httponly"]
);
}
// Finally, destroy the session.
@session_destroy();
@session_regenerate_id();
?>
so now where i add these codes? my orders are overwriting with last order. i believe not checkoutsucess page