alternatekey

An alternate key in a database is a column or a set of columns that can uniquely identify a row in a table. Unlike the primary key, which is mandatory and chosen to be the main identifier for a table, an alternate key is not the primary identifier. However, it must also enforce uniqueness. This means that no two rows in the table can have the same value for the columns that constitute an alternate key.

The purpose of alternate keys is to provide alternative ways to access or identify records within a table. For example, in a table of customers, a customer ID might be the primary key. However, a customer's email address could also uniquely identify them. Therefore, the email address column could be designated as an alternate key. This allows for efficient searching and retrieval of customer data using either the customer ID or their email address.

When defining an alternate key, a unique constraint is typically applied to the relevant column(s). This constraint ensures that duplicate values are not allowed. Databases often allow for multiple alternate keys to be defined within a single table. The selection of which key to use as the primary key is a design decision, often based on factors like data stability, performance, and ease of use. Alternate keys provide flexibility and redundancy in data identification and access.