Materialization and the Optimizer Fence

Concepts covered: sqlRecursiveCte

Recursive CTEs are the only standard SQL syntax for iteration. The engine runs an anchor query, then iterates a recursive step until no new rows are produced. The shape is the same across engines: WITH RECURSIVE name AS (anchor UNION ALL recursive_step). Past the basics, the question is rarely about syntax. It is about when to reach for recursion at all, and when a window function or self-join is cleaner. The canonical recursive shape Three pieces. The anchor produces the starting row. The recursive step produces the next row by referencing the CTE itself. The WHERE clause inside the recursive step is the termination condition; without it, the recursion runs until the engine's recursion limit. The UNION ALL combines the anchor and all iterations into the final result. This is the date-spin

About This Interactive Section

This section is part of the CTEs (Common Table Expressions): Intermediate lesson on DataDriven, a free data engineering interview prep platform. Each section includes explanations, worked examples, and hands-on code challenges that execute in real time. SQL queries run against a live database. Python runs in a sandboxed Docker container. Data modeling problems validate against interactive schema canvases. All content is framed around what data engineering interviewers actually test at companies like Meta, Google, Amazon, Netflix, Stripe, and Databricks.

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