Second Normal Form (2NF)
Second normal form eliminates, on top of 1NF, partial dependencies of non-prime attributes on candidate keys; it only applies to composite candidate keys.
Purpose
To eliminate redundancy and update anomalies caused by partial dependencies.
Mechanism
If the candidate key is composite, non-prime attributes must depend on the full key, not a subset. E.g., if (student_id, course_id)→grade and student_id→name, then name partially depends on the key and belongs in the student table. Single-column-key tables satisfy 2NF automatically.
Use cases
- Database design
- Normalization
- Redundancy elimination