Interview Questions

An index is a data structure (often a B-tree) that speeds up reads by avoiding full table scans. Trade-off: it consumes storage and slows writes (inserts/updates must maintain the index), so index columns you frequently filter or join on.

Normalization organizes tables to reduce redundancy and avoid update anomalies, via normal forms (1NF–3NF/BCNF). It improves data integrity but can require more joins; denormalization is sometimes used for read performance.

Atomicity (all-or-nothing transactions), Consistency (valid state transitions), Isolation (concurrent transactions don't interfere), Durability (committed data survives crashes). They guarantee reliable transaction processing in relational databases.