What is a subquery and when would you use it?

Short answer: A subquery is a query within a query. It is used to retrieve data that will be used in the main query. Use case: Filtering: When the result of a subquery is used to filter data in the outer query. Aggregation: When the result of the subquery is used in aggregate functions.

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.