Third Normal Form (3NF): Nothing But The Key
Third Normal Form (3NF) dictates that every non-key column must describe 'nothing but the key.' This prevents transitive dependencies, where one non-key column determines another.
Third Normal Form (3NF) ensures every non-key column provides a fact about 'nothing but the key.' This means no non-key column can depend on another non-key column, only on the primary key itself. This prevents update anomalies; if a department's name is in an employee table, changing it requires updating many rows. The common footgun is confusing 3NF's focus on transitive dependencies (non-key -> non-key) with 2NF's focus on partial dependencies (part of a key -> non-key).
Read the original → Wikipedia: Third normal form
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