[opmac]

In a database like MySQL where a clustered index exists for the primary key, or even a NoSQL DB like DynamoDB, it often makes sense to expose some version of the PK to the public if your lookup pattern for that resource is going to be by PK --- versus having some other "public" primary key field like you describe.

If you look up the resource by some other field, that means that you now need to support two indexes - one for the primary key, and one for the "public" primary key. This obviously requires more storage and comes with the performance overhead of keeping the second index updated on modifications to the table. Additionally, for something like DynamoDB where you pay per index, it could be cost prohibitive.

A better pattern is to simply encrypt/decrypt the primary key before exposing it publicly, such as in a URL. This requires no additional database overhead.