2NF

Second Normal Form (2NF) is a database normalization standard that applies to relational schemas. A relation is in 2NF if it is in 1NF and every non-prime attribute is fully functionally dependent on every candidate key. A functional dependency X -> Y is full if removing any attribute from X makes the dependency no longer hold. A partial dependency occurs when a non-prime attribute depends on part of a candidate key. Prime attributes are those that are part of any candidate key. If a relation has no composite candidate key, it is automatically in 2NF.

Consider a relation Enrollments with attributes StudentID, CourseID, StudentName, CourseTitle, Grade. The candidate key is (StudentID, CourseID). StudentName depends on StudentID and CourseTitle depends on CourseID, which are partial dependencies, thus the table is not in 2NF. Decompose into Student(StudentID, StudentName), Course(CourseID, CourseTitle), and Enrollment(StudentID, CourseID, Grade). Now Grade depends on the whole key (StudentID, CourseID) in Enrollment, satisfying 2NF.

2NF is a stepping stone in normalization. It removes partial dependencies of non-prime attributes on candidate keys, but it does not address transitive dependencies, which higher normal forms such as 3NF and BCNF handle. In practice, 2NF helps reduce update anomalies by ensuring that non-prime attributes rely on the entire candidate key rather than part of it.