populate now has its own code path to apply changes to the view. It was
okay until now because all we do is filter. But now that we are also
applying aggregations, we'll end up with two disjoint code paths.
A better approach is to just apply the results of our select to the
delta set, and apply it.
This is just the bare minimum that I needed to convince myself that this
approach will work. The only views that we support are slices of the
main table: no aggregations, no joins, no projections.
drop view is implemented.
view population is implemented.
deletes, inserts and updates are implemented.
much like indexes before, a flag must be passed to enable views.
