Combo box "Select Category"

As a lot of users, I find 'joodb' very usefull extension of Joomla. I work with Joomla 2.5 and I've instaled without the problem the last version of 'joodb'. And it works.
But... On the sample page of 'joodb' we can see a great exemple of joodb table in catalog view. And there is an extra combo box which allows to choose the category of item. HOW IT IS DONE??? I spend a lot of time to find the answer. And I am note alone to ask this question. Maybe is a secret part of future version? If not let us know how to add this combo box to the catalog view of data base.
Dirk, be cool and reveal this mystery.
Regards

{joodb groupselect|category}

Super!!! It works! Thank you for your answer. Finally it's easy to do.
I have another question. Now, when I can see my Catalog View (with the combo Select Category :-)), I'd like to improve the Single Entry View. I've added some styles in this template and the result is OK. I'd like to add the possibility to navigate in the single entry view. I mean, add the link to the next and previous entry, and to the first and last. In the Catalog View we can find this function to navigate between the pages of the catalog. Why not in the single entry view??? Any idea? It's possible?