Kandidatnøgler

Kandidatnøgler, or candidate keys, are a fundamental concept in relational database theory. A candidate key is a set of attributes in a relation (table) that uniquely identifies each tuple (row) within that relation. This means that for any two distinct rows in the table, the combination of values in the candidate key's attributes must be different.

Crucially, a candidate key must satisfy two properties: uniqueness and minimality. Uniqueness ensures that no two rows share the same candidate key values. Minimality means that no proper subset of the candidate key can also uniquely identify all rows. If a subset of a candidate key could uniquely identify rows, then that subset would itself be a candidate key, and the original set would not be minimal.

A relation can have multiple candidate keys. Among these candidate keys, one is typically chosen as the primary key. The primary key serves as the principal means of identifying rows and is used for establishing relationships between tables. Other candidate keys that are not chosen as the primary key are called alternate keys.

The concept of candidate keys is essential for ensuring data integrity and facilitating efficient data retrieval in relational databases. By enforcing unique identification, candidate keys prevent duplicate records and provide a reliable mechanism for referencing and linking data across different parts of a database. The identification of candidate keys is a crucial step in database design and normalization.