SQL Mastery: Using Window Functions for Top N Per Group (ROW_NUMBER, RANK, DENSE_RANK) SQL Mastery: Using Window Functions for Top N Per Group (ROW_NUMBER, RANK, DENSE_RANK) The "Top N per Group" problem is a core challenge in "SQL Mastery". "Window Functions", particularly the ranking functions used with the "PARTITION BY" clause, provide the most efficient, elegant, and standard way to retrieve the highest-ranking records within any category. In "database management" and "data science", one of the most common analytical queries is finding the "Top N" records for distinct categories—for example, "the top 5 highest-selling products in each region," or "the 3 most recent user logins for every user ID." Attempting this with traditional `GROUP BY` and aggregate functions is impossible without highly complex and ineffi...