Clickhouse is a column store designed for analytics [OLAP] workloads. It would compete with, say, Apache Druid or Apache Pinot.
ScyllaDB is a wide column store which is, in fact, a row store; you can call it a "key-key-value," since it had a partitioning key and a clustering [or "sort" key]. Which is more for transactional workloads [OLTP]. So it is more comparable with Cassandra or DynamoDB.
So they are really designed for different sorts of things.
That being said, ScyllaDB has some features, like Workload Prioritization, so you can run analytics, like range or full table scans against it without hammering your incoming transactions. But it wasn't designed specifically for that.
ScyllaDB is a wide column store which is, in fact, a row store; you can call it a "key-key-value," since it had a partitioning key and a clustering [or "sort" key]. Which is more for transactional workloads [OLTP]. So it is more comparable with Cassandra or DynamoDB.
So they are really designed for different sorts of things.
That being said, ScyllaDB has some features, like Workload Prioritization, so you can run analytics, like range or full table scans against it without hammering your incoming transactions. But it wasn't designed specifically for that.