What is required for data to be in Third Normal Form (3NF)?

To achieve Third Normal Form (3NF), it is essential that the data meets specific criteria. First, the data must already be in Second Normal Form (2NF), which means it eliminates partial dependencies; in other words, all non-key attributes must be fully functionally dependent on the entire primary key.

In 3NF, an additional condition is applied: all non-key fields must be directly dependent only on the primary key and not on other non-key attributes. This ensures that each piece of information is stored in such a way that its removal would not affect the integrity of the data related to the primary key.

Ensuring that fields depend solely on the primary key helps prevent redundancy and update anomalies, making the database structure more efficient and reliable. This principle underscores the importance of data integrity in database design, allowing for simpler maintenance and clearer relationships between fields.

The other options do not meet the necessary conditions for 3NF. For example, having duplicate values would violate normalization principles instead of supporting them, while insisting all records be stored in a single table ignores the relational design that normalization seeks to achieve. Similarly, inconsistent data types would compromise the integrity of the database, undermining the very goals of normalization.