SQL Alternative Key

SQL Alternative Key?

Alternate Keys in an SQL database table are candidate keys that are not presently selected as the primary key. They serve to uniquely identify a tuple (or record) within a table.

Syntax

There is no dedicated query or syntax to establish the alternate key in a table. It simply refers to a column that is a strong contender as a secondary option for the primary key designation. Consequently, these keys are also referred to as secondary candidate keys.

Features of Alternate Keys

1) Uniqueness:

Alternate keys do not tolerate duplicate values, ensuring data integrity.

2) Multiplicity:

A table can boast more than one alternate key, allowing for diverse data identification mechanisms.

3) NULL Values:

Unless the NOT NULL constraint is explicitly set, alternate keys can contain NULL values.

4) Candidate Key Relationship:

While all alternate keys are candidate keys, the reverse isn't true. each candidate key may not be an alternate key.

5) Exclusion of Primary Key:

The primary key, also a candidate key, cannot be considered an alternate key.

Real world Example

To solidify our understanding, let's consider a real world example. Imagine a table named CUSTOMER_DETAILS, featuring fields like ID, NAME, EMAIL, MOBILE_NO, and address. Here, ID, EMAIL, and MOBILE_NO stand as candidate keys. If one is chosen as the primary key, the remaining two become alternate keys, providing alternative pathways for unique record identification.