Adding Categories....table join?

[eluser]afterspark[/eluser]
Hello,

I'm trying to add categories to my database application. I already have the database structure set up like so....

articles
-ID
-Name

categories
-ID
-Name

articlecategories
-articleID
-CategoryID

Before I added the categories I'd been using this query to get the results from my database

Code:

$query2 = $this->db->getwhere('articles', array('articleSlug' => $this->uri->segment(2)));

Now I need to add to the query something that will identify the articleID and then query the other tables to bring back the categories assigned to the article.

I'm new to this so I'm a little stuck at this point. Any help would be greatly appreciated.