Zoom query for assets unplanned

Hi,
I made a session where assets can be planned as hired. Therefore I made a new table where a Date from - to is entered in which time period the asset is given away.
My problem is that when a new give away is planned the zoom to session should be filtered to only the assets that are available (check current date first, make a query on the custom table which assets are already taken in that period and then skip these records in the zoom session)
I really have no idea how to do that.