[radiowave]

The only option that Postgres's materialized views give you is to "refresh" the view, meaning: re-run the query used to define the view, fetching an entirely new dataset, and use that to replace all the existing data in the view.

There's no facility for deltas, or any other way of propagating changes.

Edit: And to answer your original question, yes you can absolutely base the materialized view on data obtained from a foreign table.