How do transactions affect concurrent operations in a database?

Short answer: Transactions impact concurrent operations by introducing locking mechanisms to ensure that multiple transactions don't interfere with each other and cause inconsistent data.

Explain a bit more

This affects concurrency in several ways: Locking: Transactions may lock rows or tables to prevent conflicting changes, leading to possible delays for other transactions. Deadlocks: When two or more transactions are waiting for each other to release locks, causing a cycle of dependency. This can be automatically detected and resolved by the DBMS.

Real-world example (ShopNest)

Checkout wraps stock decrement + order insert in a transaction so you never sell stock you do not have.

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.