It does not handle deletes / updates of the source table at all - it means the data of the materialized view become unaffected. Nothing sophisticated... About

It does not handle deletes / updates of the source table at all - it means the data of the materialized view become unaffected. Nothing sophisticated... About the multi-level aggregate queries - the only way is to define a materialized view for the inner query and do calculations on top of it on the fly. So, the data for the inner query will be pre-aggregated, but nothing on top of that.