SELECT all sprites the user DONT have

I have a feature in my webstie that the users can receive items.
I have a table with the list of items and what’s the user_id they are belong to - very simple table:

id | user_id | item_id

Sometimes the user may receive an item.
My problem is, that the user can’t get the SAME item twice.
so I need to change this query:

$getrandom = mysql_fetch_assoc(mysql_query('SELECT id,name FROM `items`  ORDER BY RAND()'));

which gives a random item from all items, instead picking ONLY the items the user don’t have (check in the user-item table if he got the item).

I need to filter the items this user has already got. the user id is storred in my session as $_SESSION[‘id’].

Looking for assistance with this. Thanks in advance!

  FROM items
  JOIN user_items
    ON user_items.item_id =
   AND user_items.user_id = $_SESSION['id']
 WHERE user_items.user_id IS NULL

@theunreal; are you aware that the old mysql_* extension has been deprecated as of version 5.5 of PHP and will very likely be removed from version 5.6 of PHP? You should be migrating over to either the mysqli_* extension or PDO