How to import this xml feed into sql with auto update?

I have a little problem and i cant find any results on internet.

My boss have a xml feed from his products provider and he asked me to insert all data from xml link into mysql website db.

So i begin like this:

#database
$sql= new MySQL();
//connect to db   
$host = 'localhost';   
$user = 'user';   
$pass = 'pass';   
$db = 'dbname';     

$sql = mysql_connect ($host, $user, $pass) or die           ("Error - Unable to Connect");     

mysql_select_db($db) or die ("Error- Unable to find database");                     

// specify url of xml file   

$url = "thehttpofurlproducts";         

// get xml file contents   

$xml = simplexml_load_file($url);   

foreach ($xml->Items->Item as $item) {

$query = "INSERT INTO products (id,code,info) VALUES ($item->prod_id, $item->prod_code,$item->prod_info)";
   $result = mysql_unbuffered_query($query) or die ("Error in query: $query. ".mysql_error());

}  
 mysql_close($connection);

And there are many others fields he wanted me to import into sql db. He want to make this run in real time so i use cronjobs. But the problem is how to update the products in realtime . When i run this second time it gives me errors like duplicate key, etc.

The xml is like this and its continously update :

<Message>
<EntityType>Products</EntityType>
<Items>
<Item>
<prod_id>235</prod_id>
<prod_code>xzq</prod_code>
<prod_name>Dogs</prod_name>
<prod_info><prod_info/>
<isstoc>false</isstoc>
<UM>UM</UM>
<VAT>20.00</VAT>
<prod_category>Puppies</prod_category>
<prod_subcategory>--</prod_subcategory>
<Onlineprice>0.00</Onlineprice>
<Stock>0.00</Stock>
<Weight/>
</Item>
</Items>
</MESSAGE>