[benesch]

So, roughly speaking, I think you're describing a view that could be defined in Materialize like so:

    CREATE MATERIALIZED VIEW customer_avg_latency
    SELECT customer_id, metric_id, avg(metric_val)
    FROM metrics
    JOIN resources ON metrics.resource_id = resources.id
    JOIN customers ON resources.customer_id = customer.id
    GROUP BY customer_id, metric_id

There are various ways to slice and dice that query as a user that'll allow you to choose whether to do the aggregate early or late. The details, I think, depend on the specifics of your data model.

> When a resource migrates between customers, the whole history of the customer changes.

I'm a bit confused about this part. In the query I posted above, Differential's incremental join algorithm would spare you from recomputing the entire join. (As written the query would have to re-aggregate the metrics associated with that resource that moved, but that could be solved by manually pushing the avg down.)

If you'd like to drop by our Community Slack (https://materialize.com/s/chat) or GitHub issues (https://github.com/MaterializeInc/materialize/issues) we'd be happy to talk through things in more detail!