What additional requirement does Second Normal Form (2NF) impose compared to First Normal Form (1NF)?

Second Normal Form (2NF) builds upon the requirements of First Normal Form (1NF) by adding a critical condition regarding how data dependencies are structured within a database. Specifically, 2NF requires that all non-primary key attributes must be fully functionally dependent on the entire primary key.

In practical terms, this means that if you have a composite primary key (a primary key made up of two or more columns), every non-primary key attribute in that table must depend on the entirety of that composite key rather than just a portion of it. This ensures that there are no partial dependencies, which helps eliminate redundancy and maintain data integrity. By enforcing this rule, 2NF effectively reduces the amount of duplicate data in the database and enhances the logical organization of data.

In contrast, the other options address different aspects of database design that do not directly pertain to the additional requirements specified by 2NF. For instance, ensuring that each row is unique is a hallmark of 1NF. Similarly, having all data stored in separate tables relates more to database normalization in general, and while tables must have a primary key in a well-structured database, this requirement applies uniformly across all normal forms, not just 2NF.