Normalization To Third Normal Form
Normalization organizes columns so that each fact is stored exactly once. Redundant facts cause update anomalies, where changing a value in one place leaves stale copies elsewhere. The first three normal forms remove the most common redundancy.
First normal form requires that every column hold a single atomic value, with no repeating groups or lists in a cell. A column packed with three phone numbers violates it. You split such data into separate rows or a related table.
Second normal form applies when the primary key is composite. It requires that every non key column depend on the whole key, not just part of it. If a column depends on only one part of a composite key, it is a partial dependency and must move to its own table.
Third normal form removes transitive dependencies. A non key column must depend on the key directly, not through another non key column. If a city column determines a region column, the region is transitively dependent and belongs in a separate lookup table keyed by city.
The slogan is that every non key column depends on the key, the whole key, and nothing but the key. Reaching third normal form usually yields a clean schema where each fact lives in one place, so updates touch a single row and consistency is automatic.
Key idea
Normalize so every non key column depends on the key, the whole key, and nothing but the key, eliminating redundancy and update anomalies.