Which of the following describes a candidate key?

A candidate key is defined as a set of attributes that can uniquely identify a record in a database table. This means that each candidate key has the essential quality of ensuring that no two records can share the same value for the attributes included in that key. Each table can potentially have multiple candidate keys, and one of those keys will typically be chosen as the primary key, which is used to enforce entity integrity within that table.

The concept behind a candidate key is vital in the context of relational database design as it helps maintain data integrity and ensures that each record can be distinctly accessed without ambiguity. This uniqueness is crucial for efficiently retrieving and managing data.

In contrast, other options provided do not accurately capture the definition of a candidate key. For instance, referring to an attribute used for foreign keys does not convey the uniqueness aspect that defines candidate keys. Automatically generated keys, such as surrogate keys, serve a different purpose and are not inherently candidate keys unless they can uniquely identify records. Lastly, a non-unique identifier does not align with the concept of a candidate key, as its primary characteristic is its ability to ensure uniqueness within a dataset.