I picked a query I'd written for a funnel analysis and started explaining it, but I fumbled the join explanation partway through.
Select a genuinely complex query you've written, ideally involving multiple joins, subqueries, window functions, or CTEs. Structure your answer by first stating the business problem, then walking through the query's logic step-by-step, highlighting the key SQL concepts and join types used. Emphasize the impact and any optimizations you made.
Pro tip: Quantify the impact: mention how the query improved a metric (e.g., reduced runtime from hours to minutes, enabled a new analysis) to show you understand the business value, not just the technical details.
Briefly describe the business problem or analytical question the query addressed, and why it was complex (e.g., data volume, multiple sources, intricate logic).
Give a high-level overview of the query's components: CTEs, subqueries, main SELECT, and any window functions or aggregations.
Detail the join types used (INNER, LEFT, FULL OUTER, etc.), why each was chosen, and how they combined data from different tables.
Discuss advanced concepts like window functions, recursive CTEs, pivoting, or performance tuning (indexes, query plans) that were crucial.
Describe the query's impact (e.g., performance, insights) and any lessons learned or optimizations applied.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.