In which cases is it recommended to use natural keys in a database?

Natural keys in a database are keys that already exist in the domain and uniquely identify a record (e.g., passport number, TIN, email).

It is recommended to use natural keys when:

• The key value is stable and does not change over time.
• The key is truly unique and unambiguously identifies the record.
• The key is short and simple for indexing.
• There is no need for an additional surrogate key (e.g., auto-increment ID).

For example, in a user table, email can serve as a natural key if it is unique and does not change.

However, if the natural key can change or is complex, it is better to use a surrogate key.