[Nican]

I know nothing about ClickHouse, but how many cores are being used for these queries? And what is the core processing frequency?

I would think ClickHouse is tuned for analytics workloads, so it will throw plenty of cores at the problem, and not care much for the overhead. Meanwhile, I believe PostgreSQL is more tuned to transactional workloads, where it will not pay the query parallelism overhead, but optimize for multiple parallel workloads.