What is an Index and why would you use it?

Short answer: An Index is a database object that speeds up the retrieval of rows from a table by creating a data structure (often a B-tree). Indexes improve the performance of SELECT queries but can slow down INSERT, UPDATE, and DELETE operations.

Example code

CREATE INDEX idx_employee_name ON Employees(Name);

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.