Can you explain the concept of a composite index?

Short answer: A composite index is an index that involves more than one column in a table. It's used when queries often filter or sort by multiple columns, optimizing performance for those specific queries.

Real-world example (ShopNest)

ShopNest adds an index on Orders(CustomerId, CreatedAt) because “my recent orders” is queried constantly.

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.