What are Window Functions in SQL?

Short answer: Window functions allow you to perform calculations across a set of table rows that are related to the current row, without collapsing the result set into a single row.

Example code

ROW_NUMBER() generates a sequential integer to each row within the result set. Example: SELECT name, salary, ROW_NUMBER() OVER (ORDER BY salary DESC) AS row_num FROM employees; This query adds a sequential row number to each employee, ordered by salary.

Real-world example (ShopNest)

ShopNest’s SQL Server database stores customers, products, and orders. Good indexes and clear foreign keys keep checkout queries fast and safe.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.