Talking Through Top-N in an Interview

Concepts covered: sqlRankDenseRank

Past the basic solution, the interviewer probes business semantics and operational reality. 'What if there's a tie at position N?' is the semantic probe. 'How does this perform on a billion rows?' is the operational probe. Both have crisp answers if you know them. Exactly N vs at-least N: the business semantics probe Suppose the question is 'top 3 highest-paid employees per department.' Now imagine Engineering has Alice ($200k), Bob ($180k), Carol ($180k), Dave ($150k). Carol and Bob are tied for second. Do we return 2 rows, 3 rows, or 4 rows from Engineering? The answer depends entirely on the business rule, and the interviewer wants to hear you ask. Performance: indexes and partitioning Window functions are not magic. ROW_NUMBER() OVER (PARTITION BY department_id ORDER BY salary DESC) re

About This Interactive Section

This section is part of the Top N Per Group: Beginner 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.

How DataDriven Lessons Work

DataDriven combines four interview rounds (SQL, Python, Data Modeling, Pipeline Architecture) with adaptive difficulty and spaced repetition. Easy problems get harder as you improve. Weak concepts resurface until you master them. Your readiness score tracks progress across every topic interviewers test. Every lesson section ends with problems you solve by writing and running real code, not by picking multiple-choice answers.