Self-Joins on Large Tables and Indexing

Concepts covered: sqlRecursiveCte

The escalation past hierarchy walking is multi-relationship traversal. Employees report to managers and are also part of project teams; the question becomes 'find every employee within two relationship hops from employee 42 in either direction.' The same recursive CTE shape generalizes, but the recursive step's join condition encodes multiple relationship types. This section is the depth signal at the staff level: can you reason about graph algebra expressed in SQL? Multi-edge recursion The recursive step's ON clause unions multiple edge types. The result is the set of employees reachable from employee 42 within 3 hops, where 'reachable' is defined by either the reporting relationship or the project-team relationship. The same idea extends to any graph encoded across one or more tables; th

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This section is part of the Self-Join: 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 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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