Kandidatnøglerne

Kandidatnøglerne, or candidate keys, are a fundamental concept in relational database theory. A candidate key is an attribute or a set of attributes that can uniquely identify a tuple (row) within a relation (table). This means that for any given candidate key, no two rows in the table can have the same values for that key.

A relation can have multiple candidate keys. Among these candidate keys, one is chosen as the primary key. The primary key is then used as the main identifier for rows and is crucial for establishing relationships between tables through foreign keys. While the primary key must be unique and non-null, candidate keys are not necessarily required to be non-null. However, if a candidate key is intended to be used as a primary key, it must satisfy the non-null constraint.

The concept of candidate keys ensures data integrity by preventing duplicate records. By defining and enforcing candidate keys, databases can maintain a consistent and reliable state. Identifying all candidate keys is an important step in database design and normalization, helping to achieve an optimal relational schema.