Little bit hazy because it was 15 years ago. I’d used an external int id that was syncing down into our system. There were then a bunch of other tables referen

Little bit hazy because it was 15 years ago. I’d used an external int id that was syncing down into our system. There were then a bunch of other tables referencing it as a foreign key. Overnight it turned into a sting. Clearly I was going to have some reconciliation work to do in any case and it may be that I maintained the old id as the primary key at that point (can’t recall). It was just a good lesson in mitigating the blast radius - especially wrt things that are out of your control. As an analogy, imagine that you’re dealing with dates in the same system (we were), you wouldn’t let their date format bleed into your other tables. You draw a line at the boundary between the systems. In a way, natural keys break that rule.