What characterizes a Primary Key in a database table?

A Primary Key in a database table is a critical aspect of relational database design. It uniquely identifies each record in a table, ensuring that no two rows can have the same primary key value. The defining characteristic of a Primary Key is that every row in the table must contain a key value, which cannot be duplicated across rows. This ensures the integrity and uniqueness of each record.

When considering the correct answer, it specifically states that every row must contain a key value, which inherently establishes that this value has to be unique to that particular row. This uniqueness is paramount for operations such as searching and relating tables through foreign key relationships.

The other provided choice suggesting that all key values are unique but not every row contains a key value is inconsistent with the definition of a Primary Key, as it requires every row to have a key. Similarly, having duplicate values or randomly filled values in the key column directly contradicts the foundational principles of how Primary Keys are defined and used to maintain data integrity.