subkeys

Subkeys, also known as secondary keys or alternate keys, are fields or combinations of fields within a database table that can uniquely identify a record, but are not designated as the primary key. While a primary key is the main identifier for a record and must be unique and non-null, subkeys provide alternative ways to access or reference data. They are often used for business logic requirements or to improve query performance by creating indexes on frequently searched columns.

A subkey may or may not enforce uniqueness depending on the specific database system and design. If a subkey is designed to be unique, it functions similarly to a unique constraint, preventing duplicate values from being entered into that field or combination of fields. This is useful for ensuring data integrity when multiple attributes could logically serve as identifiers.

Implementing subkeys typically involves creating indexes on the relevant columns. These indexes allow the database management system to quickly locate records based on the values in the subkey fields, even if they are not the primary means of identification. This can significantly speed up search and retrieval operations. For example, in a table of customers, a customer ID might be the primary key, while an email address or a social security number could be designated as subkeys, especially if uniqueness is enforced for these fields. The choice to use subkeys depends on the anticipated data access patterns and the need for alternative identification methods within the database.