What is database normalization and why does it matter?

The normal forms are rules about dependencies. First normal form removes repeating groups and requires atomic values. Second normal form removes partial dependencies on part of a composite key. Third normal form removes transitive dependencies between non-key columns.

CREATE TABLE customers (
  id BIGINT PRIMARY KEY,
  email TEXT NOT NULL UNIQUE
);

CREATE TABLE orders (
  id BIGINT PRIMARY KEY,
  customer_id BIGINT NOT NULL REFERENCES customers(id),
  created_at TIMESTAMPTZ NOT NULL DEFAULT now()
);

What normalization buys you

• One authoritative place for each fact, so updates do not diverge
• Smaller rows and fewer contradictory copies
• Constraints can express real business rules
• Queries can combine entities through joins without duplicated state
• Schema changes are easier when data is not copied across many columns

Normalization is a default, not a religion. Highly normalized schemas can require many joins for read-heavy reporting. The usual approach is to normalize transactional data and denormalize selectively in read models or materialized views.