ClickHouse ® CTE example: How to use WITH in ClickHouse ®

Common Table Expressions (CTEs) in ClickHouse allow users to define temporary named result sets within a single query using the WITH clause, enhancing readability and reusability by breaking down complex SQL logic into manageable parts. CTEs are particularly beneficial for filtering data in stages or when the same intermediate calculation is needed multiple times in a query, reducing code duplication and improving maintainability. ClickHouse supports both non-recursive and limited recursive CTEs, with the latter allowing iterative calculations under specific constraints. While CTEs are materialized in memory during query execution, making them suitable for small to medium datasets, they might consume significant memory for larger datasets. In comparison with subqueries and materialized views, CTEs are ideal for multi-stage filtering or aggregation within a single query, while subqueries are better for single-use intermediate results, and materialized views are optimal for pre-computed, frequently used aggregations. Tinybird, a managed ClickHouse service, offers an alternative with multi-node pipes, providing modular and reusable querying capabilities that improve upon the limitations of traditional CTEs by facilitating within-pipe and cross-project reusability, independent testing, and better debugging.