Good point. If you just want to copy data far and away the easiest way to transfer data is using MySQLDatabaseEngine. You can even copy table definitions. Watch for issues with Decimal datatypes if you do this.

Be careful with this engine, it's easy to accidentally expose the password as you only need table read permissions if it wasn't set up using an external credential file.

https://github.com/ClickHouse/ClickHouse/issues/3311

I also had some pretty bad join performance (CH table joined to MySQL table), the quick solution to both of these is that we instead use the table function (https://clickhouse.com/docs/en/sql-reference/table-functions...) to copy the data periodically.

Use Named Collections to protect credentials. They are very handy. Here's an article that discusses use in the JDBC Bridge.

https://altinity.com/blog/connecting-clickhouse-to-external-...

Disclaime: I work for Altinity.