What is database normalization and why does it matter?
Reported in N26 European engineering loops. DBMS fundamentals covering 1NF through 3NF and when to denormalize.
Interview scenario
Often asked in N26 loops at European offices (London, Berlin, Amsterdam, Paris, Stockholm, Dublin, and remote EU). Prepare a clear spoken answer plus key trade-offs.
Model answer
Try answering aloud first
Cover trade-offs, structure, and a concrete example before revealing the baseline response.
How to frame this at N26: Connect your answer to measurable impact, clarity of thought, and trade-offs the team cares about. Below is a strong baseline response you can adapt with your own project examples.
Normalization is the process of organizing tables to reduce redundancy and update anomalies. Each fact should live in one place so inserts, updates, and deletes stay consistent.
1NF: atomic columns, no repeating groups. 2NF: no partial dependency on a composite key—all non-key columns depend on the entire primary key. 3NF: no transitive dependency—non-key columns depend only on the key, not on other non-key columns.
Example: storing department name on every employee row violates 3NF if department name depends on dept_id alone—split into departments and reference by foreign key.
Denormalization is intentional duplication for read performance (analytics, caching). Interviewers want you to normalize first, then justify controlled denormalization with measured query patterns.
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