What are aggregate functions in SQL?

Short answer: Aggregate functions perform a calculation on a set of values and return a single value. Common aggregate functions include: COUNT(): Returns the number of rows. SUM(): Returns the sum of a column. AVG(): Returns the average of a column. MAX(): Returns the maximum value. MIN(): Returns the minimum value.

Example code

SELECT AVG(salary) FROM employees;

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.