Simplest way for you would be to use the option binders.
1. Add a new drop down list to your form
2. Choose an option binder when configuring your field
3. The easiest to use would be the SQL binder which allows you to just key in your query language. The SQL binder is available if you're a subscriber.
4. Alternatively you could use the beanshell binder which requires you to manage your own connection and datasource objects thru java code. Remember to return the FormRowSet object if you're going this route.
Either way should work fine tho.