How do you find the top-N rows per group using window functions?

Use ROW_NUMBER() with PARTITION BY: SELECT * FROM (SELECT *, ROW_NUMBER() OVER (PARTITION BY dept_id ORDER BY salary DESC) AS rn FROM employees) ranked WHERE rn <= 2. How it works: ROW_NUMBER() assigns 1 to highest salary per department, 2 to second highest, etc. The outer WHERE rn <= 2 keeps only the top 2 per department. Why ROW_NUMBER over RANK: if two employees tie at the same salary, RANK wou