I don’t think you’re going to find any expression functions that will let you work with datasets in the way that you want to. They are pretty limited that way.
Your best bet, in my opinion, is to store all your data from the query in a dataset custom property on the root container, or anywhere else that is useful for you, and use a property change event on that dataset property to build the two datasets for each of your two tables. Any time the dataset gets new data (ie. your where clause changes) the two tables will automatically get populated with new data (no need for extra buttons, etc.)