Support Cassandra as External Dictionary Source

Why it matters

This feature enables users to load dictionary data from Cassandra databases, allowing seamless integration of Cassandra-stored data into ClickHouse queries and analytics. It solves the problem of lacking native support for Cassandra as a dictionary source, thus expanding ClickHouse's connectivity and data enrichment capabilities.

How to use it

To use Cassandra as an external dictionary source, define a dictionary with the cassandra source type in the dictionary configuration XML file, specifying the necessary connection parameters such as host, port, keyspace, and table. Then, load the dictionary as usual in ClickHouse to enable lookups from Cassandra.