Unikhetsbegränsning

Unikhetsbegränsning is a Swedish term that translates to "uniqueness constraint" in English. It is a fundamental concept in database management and relational algebra. A uniqueness constraint ensures that the values in one or more columns of a table are unique. This means that no two rows in the table can have the same combination of values for the specified columns.

The primary purpose of a uniqueness constraint is to maintain data integrity. By enforcing uniqueness, it prevents duplicate records from being inserted into a database, which can lead to errors, inconsistencies, and difficulties in data retrieval and analysis. For example, in a table of customers, a uniqueness constraint on the email address column would ensure that each customer has a distinct email address, preventing the same person from being registered multiple times with the same contact information.

Uniqueness constraints can be applied to a single column (a simple unique constraint) or to a combination of columns (a composite unique constraint). If applied to a single column, it guarantees that each value in that column is distinct. If applied to multiple columns, it guarantees that the combination of values across those columns is unique for each row.

Implementing uniqueness constraints is typically done through database schema definitions. When creating or altering a table, developers can specify which columns should have a uniqueness constraint. The database management system then enforces this constraint automatically, raising an error if an attempt is made to insert or update data that violates the constraint. This proactive approach to data integrity is a cornerstone of robust database design.