What is a composite key?

Short answer: composite key is a combination of two or more columns in a table that can uniquely identify each record in the table. It is used when a single column is not sufficient to uniquely identify a row.

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.