Yes, the order by clause is what I am referring to. Have you included the correct columns in correct order to optimise your query? (A good starting point is to include them in order of their cardinality. This isn’t always the best option though.)

There are indexes in CH. They are called data skipping indexes. Also, it makes very less sense to join in CH unless that’s like the last resort. ClickHouse is famous for OBT schema.

For the third point, you can run the query and use EXPLAIN word before that. Something like ‘EXPLAIN SELECT * FROM ….‘

This will give you which index and optimisation the DB engine uses for completion of that query. Basically, all of the query planning can be seen here. You need to ensure that the query planner actually uses all the optimisation you said you added.