Which statement best describes 2NF (Second Normal Form) in relational databases?

Which statement best describes 2NF (Second Normal Form) in relational databases?

• A. 2NF removes all functional dependencies.
• B. 2NF aims to remove partial dependencies on composite keys.
• C. 2NF increases redundancy.
• D. 2NF is about indexing.

Answer: (B)

2NF focuses on removing partial dependencies that appear when a table has a composite key. In a relation with a key made of more than one attribute, a partial dependency exists if a non-prime attribute (one that is not part of any candidate key) depends only on part of that composite key rather than on the whole key. 2NF eliminates those partial dependencies by splitting the table so that each non-prime attribute is fully functionally dependent on the entire candidate key. This is why the statement describing 2NF as aiming to remove partial dependencies on composite keys is the best description. It captures the practical effect of 2NF: reducing redundancy caused by attributes tied to just part of a composite key. For example, if a table has (StudentID, CourseID) as a composite key and StudentName depends only on StudentID, that’s a partial dependency. Splitting into separate relations like Students(StudentID, StudentName) and Enrollments(StudentID, CourseID, Grade) removes that partial dependency. Other options aren’t correct because 2NF does not remove all functional dependencies, it does not increase redundancy (it reduces it), and it isn’t about indexing.

2NF focuses on removing partial dependencies that appear when a table has a composite key. In a relation with a key made of more than one attribute, a partial dependency exists if a non-prime attribute (one that is not part of any candidate key) depends only on part of that composite key rather than on the whole key. 2NF eliminates those partial dependencies by splitting the table so that each non-prime attribute is fully functionally dependent on the entire candidate key.

This is why the statement describing 2NF as aiming to remove partial dependencies on composite keys is the best description. It captures the practical effect of 2NF: reducing redundancy caused by attributes tied to just part of a composite key. For example, if a table has (StudentID, CourseID) as a composite key and StudentName depends only on StudentID, that’s a partial dependency. Splitting into separate relations like Students(StudentID, StudentName) and Enrollments(StudentID, CourseID, Grade) removes that partial dependency.

Other options aren’t correct because 2NF does not remove all functional dependencies, it does not increase redundancy (it reduces it), and it isn’t about indexing.