NebenSchlüsseln

NebenSchlüsseln, often translated as "secondary keys" or "alternative keys," is a concept used in database management systems. It refers to a column or a set of columns in a table that uniquely identifies each row, but is not designated as the primary key. While the primary key is essential for establishing the main identity of a record, NebenSchlüsseln provide alternative ways to reference and retrieve that same record.

The primary purpose of a NebenSchlüssel is to ensure uniqueness for data that might be referenced in multiple contexts or for business rules that require specific fields to be unique, even if they aren't the primary identifier. For instance, in a customer table, a customer's primary key might be a system-generated customer ID. However, a NebenSchlüssel could be the customer's email address, as it should also be unique for each customer, and is often used for login or communication.

Implementing NebenSchlüsseln typically involves defining unique constraints on the relevant columns. This tells the database system to prevent duplicate values in these columns, thus enforcing the uniqueness requirement. When querying the database, NebenSchlüsseln can be used in WHERE clauses to locate specific rows efficiently, especially if those columns are indexed.

The selection of NebenSchlüsseln depends on the specific application and data model. Common examples include email addresses, social security numbers (in jurisdictions where applicable), product serial numbers, or any other attribute that is inherently unique and useful for identification or business logic. Proper use of NebenSchlüsseln can enhance data integrity and improve query performance by providing additional access paths to data.