> If the only reason you need a surrogate key is to introduce indirection in your internal database design then sequence numbers are enough. There is no need to use UUIDs.

The UUID would be an example of an external key (for e.g. preventing crawling keys being easy). This article mentions a few reasons why you may later decide there are better external keys.

> When I come to you and say "My name is X, this is my phone number, this is my e-mail, I want my GDPR records deleted", you still need to be able to find all data that is related to me.

How are you going to trace all those records if the requester has changed their name, phone number and email since they signed up if you don't have a surrogate key? All 3 of those are pretty routine to change. I've changed my email and phone number a few times, and if I got married my name might change as well.

> Once you start thinking about your database as structured storage of facts that you can use to infer conclusions, there is much less need for surrogate keys.

I think that spirals into way more complexity than you're thinking. You get those timestamped records about "we got info about person named Y with phone number Z", and then person Y changes their phone number. Now you're going to start getting records from person named Y with phone number A, but it's the same account. You can record "person named Y changed their phone number from Z to A", and now your queries have to be temporal (i.e. know when that person had what phone number). You could back-update all the records to change Z to A, but that breaks some things (e.g. SMS logs will show that you sent a text to a number that you didn't send it to).

Worse yet, neither names nor phone numbers uniquely identify a person, so it's entirely possible to have records saying "person named Y and phone number Z" that refer to different people if a phone number transfers from a John Doe to a different person named John Doe.

I don't doubt you could do it, but I can't imagine it being worth it. I can't imagine a way to do it that doesn't either a) break records by backdating information that wasn't true back then, or b) require repeated/recursive querying that will hammer the DB (e.g. if someone has had 5 phone numbers, how do you get all the numbers they've had without pulling the latest one to find the last change, and then the one before that, and etc). Those queries are incredibly simple with surrogate keys: "SELECT * FROM phone_number_changes WHERE user_id = blah".