ClickHouse ® tips #3: the transform function

Clickhouse® enhances data handling efficiency through its JOIN engines, which offer superior performance compared to regular tables when preparing data for joins. It supports the joinGet function, enabling retrieval of table values using a key, although this cannot be applied to dynamically created data. To achieve similar performance benefits with large datasets, the transform function can be used. This approach is illustrated with a practical example involving a sales table and an exchange_rate table, demonstrating how to efficiently calculate total sales in dollars per country. The text provides guidance on replicating these performance-optimized queries using provided CSV datasets and schemas.