Kandidatnycklar

Kandidatnycklar are a fundamental concept in relational database design. A kandidatnyckel, also known as a candidate key, is a column or a set of columns in a relational database table that can uniquely identify each row. In simpler terms, it's a way to ensure that every record in a table is distinct.

For a set of attributes to be considered a kandidatnyckel, it must satisfy two main properties: uniqueness and minimality. Uniqueness means that no two rows in the table will have the same combination of values for the attributes in the kandidatnyckel. Minimality, also known as irreducibility, means that no proper subset of the kandidatnyckel can uniquely identify a row. If a proper subset could also uniquely identify rows, then that subset would itself be a kandidatnyckel, and the original set would not be minimal.

A table can have multiple kandidatnycklar. Among these, one is typically chosen as the primary key. The primary key serves as the main identifier for rows in a table and is often used for establishing relationships between tables through foreign keys. However, other kandidatnycklar, while not chosen as the primary key, are still valid unique identifiers and can be used for querying and enforcing data integrity. The concept of kandidatnycklar is crucial for maintaining the integrity and efficiency of relational databases.