Advanced MySQL 8

Almost always have an ID field

It is always recommended to use an independent ID field, even though there is an existing unique field present. For example, consider an application that was launched only for mobile users; if you look at the following table, it has mobileNumber as the primary key; as long as this schema is static and there's business use cases as well, then you wouldn't have any issues with it, apart from different sizes of mobile numbers based on locality and country.

The following diagram shows an example table of mobileNumber as an ID field:

Then, the business wanted to expand this application to email users as well, where ...