Kandidaatsleutels

A kandidaatsleutel, often translated as candidate key, is a term used in database theory. It refers to a column or a set of columns in a relational database table that can uniquely identify each row. In simpler terms, a kandidaatsleutel is a potential primary key. A table can have multiple kandidaatsleutels.

The defining characteristic of a kandidaatsleutel is that it must be minimal. This means that no proper subset of its attributes can uniquely identify the rows. If a kandidaatsleutel contains more attributes than necessary for unique identification, it is not minimal and therefore not a kandidaatsleutel.

From the set of all kandidaatsleutels, one is chosen to be the primary key for the table. The primary key serves as the main identifier for rows and is used for establishing relationships between tables. The other kandidaatsleutels that are not chosen as the primary key are called alternate keys.

For example, in a table of employees, a combination of employee ID and a combination of social security number and last name might both be kandidaatsleutels. If employee ID is chosen as the primary key, then the social security number and last name combination becomes an alternate key. Ensuring that data integrity is maintained, kandidaatsleutels are fundamental to the normalization process in database design.