Experiments on ClickHouse support

• JOIN predicates - ClickHouse does not support predicates, not comparing colums, so you can't do smth like a.Column = b.Colums AND a.Value == 2. Please use subqueries, automatic optimization supposed to bu buggy and risky.
• Subqueries as values are not supported: select (select count(*) from second) from first
• EXISTS condition is not supported
• CREATE TABLE - basic only support, prefer using direct SQL for production tables

Query settings can be configured with ClickHouseDataProvider.QuerySettings property, defaults are:

• join_use_nulls = 1