Allow to attach a database from a remote ClickHouse server, similarly to how the MySQL and PostgreSQL engines do.

All DDL queries are forwarded to the remote server. If the remote server is configured slightly differently, e.g., has a different default table engine, like in ClickHouse Cloud, these differences will be automatically used by the Remote database.

SELECT and INSERT queries will be also forwarded to the remote server, but even deeper than the Distributed table engine does. They will be processed up to the final stage, unlike the intermediate mergeable state. For this purpose, we can also introduce a Remote table engine.

Depending on the user access, it will automatically support read-only or read-write, with or without DDL statements.

Remote databases will be handy for federating multiple ClickHouse clusters or plugging a larger ClickHouse cluster into clickhouse-local or a smaller cluster.

Ultimately, we can extend it to a Cloud database engine, that will prompt sign-in to ClickHouse Cloud and create a service on demand, so you can extend any self-managed ClickHouse cluster with ClickHouse Cloud.