SQL Window Functions: Real Interview-Style Examples (Beginner → Intermediate)
Updated on February 23, 2026 11 minutes read
Frequently Asked Questions
What are SQL window functions in simple terms?
Window functions calculate values across related rows while keeping the original rows. They’re used for ranking, running totals, moving averages, and comparisons like previous/next rows.
What’s the difference between GROUP BY and window functions?
GROUP BY reduces rows into summaries. Window functions keep rows and add analytics columns, which is essential for many interview outputs
Which window functions should I learn first for SQL interview questions?
Start with ROW_NUMBER(), RANK(), DENSE_RANK(), SUM() OVER, and LAG()/LEAD(). These solve “latest per group,” leaderboards, running totals, and row comparisons.
How do I filter results from ROW_NUMBER() or RANK()?
Compute the window function in a CTE or subquery first. Then filter in the outer query using WHERE rn = 1 or WHERE rn <= N.
Do SQL window functions work in MySQL?
Yes, window functions are supported in MySQL 8.0 and later. They also work in PostgreSQL, SQL Server, Oracle, BigQuery, and Snowflake.