Composite Database

DirectQuery schema can have both external tables and in-memory Datastore tables. However, it’s important to note that joins between external tables and in-memory ones are not possible. In other words, the in-memory tables can only exist as isolated stores. In-memory tables are not directly linked to the base table.

These isolated tables can be used for instance in measures via a Copper join or via get-by-key queries. Having this data in-memory avoids a round-trip to the external database (which includes network calls) when computing the measures. For instance, if some get-by-key queries are executed for a lot of locations in a measure, having a local datastore can make the query a lot faster.