dealing with tables from different databases?

Hi. I'm a newbie to Visual Studio 2012 and stuck on how to interact with different datasets.

I am building a report that is associated with with two tables, each from a different database. Themaster_flat table with the primary key matter_number is from the first database and it contains all the columns I need that should show up in the report layout I've built. However,billing_table with the primary key matter_number contains a flag that I go by which I must use to determine whether each matter should come through in the reporting or not. 

I've set the master_flat as dataset1 and the billing_table as dataset2. Now, what is the best way in Visual studio 2012 to filter by the matters that has flag "N" in dataset2?

Thanks