ROW_NUMBER vs RANK vs DENSE_RANK

Concepts covered: sqlRankDenseRank

This section is where the question stops being about syntax and starts being about which tool to reach for. ROW_NUMBER, RANK, and DENSE_RANK look interchangeable. They are not. Each one answers a different business question, and picking the wrong one produces visibly plausible numbers that disagree with what the consumer asked for. The candidate at this level is being scored on whether they pick the right function from the answer to the clarifying question, not on whether they can recite what each function does. Three functions, three business questions The NULLS LAST move NULLs in the ORDER BY column produce silent ranking bugs. By default, Postgres puts NULLs last when sorting DESC; MySQL puts them first; SQL Server depends on the version. If you ORDER BY salary DESC and some employees h

About This Interactive Section

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