When working with analytical databases, enriching fact tables with customer information, product metadata, geographical mappings, or business attributes is a common requirement. Traditionally, this enrichment is performed using SQL JOINs.
While JOINs work well, they can become increasingly expensive as data volumes grow. Every query must repeatedly scan and match rows, adding latency and consuming valuable resources.
ClickHouse® offers a powerful alternative: Dictionaries.
Dictionaries provide a high-performance key-value lookup mechanism that allows ClickHouse to fetch reference data directly from memory without performing costly runtime JOINs. Despite being one of the most powerful optimization features available, dictionaries remain surprisingly underutilized.
In this article, we'll explore how ClickHouse Dictionaries work, when to use them, and how they can dramatically improve query performance.
