Recursive CTEs for trees

Concepts covered: sqlRecursiveCte

Multi-Level Hierarchies Self joins work for one-level relationships (employee to manager). But what if you need all ancestors: employee to manager to manager's manager to CEO? You'd need multiple self joins, and you'd need to know the maximum depth in advance. Recursive CTE Structure Recursive CTE in Practice Recursive CTEs enable traversal of arbitrary-depth hierarchies, path building, and cycle detection in graph structures. Hierarchy Example Let's find all entries under Alice (the CEO) and their level in the hierarchy: The query starts with Alice (level 1), finds her direct reports Bob and Carol (level 2), then finds their reports Dave, Eve, and Frank (level 3). It stops when no more rows reference the current level. Building a Path Recursive CTEs can accumulate information across level

About This Interactive Section

This section is part of the Joins: Advanced 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 PostgreSQL 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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