What is the difference between UNION and UNION ALL?

Short answer: UNION: Combines the result sets of two or more queries and removes duplicate rows. UNION ALL: Combines the result sets of two or more queries and includes all rows, even duplicates. Joins & Queries

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.