I don’t think that holds true in all scenarios. You need to use a key that has some guarantees. In many systems you will use data you don’t control, like email addresses, IBANs, ISBNs, passport IDs and many more. You have zero control over those keys, but because each comes with certain guarantees, they might be suitable as a foreign key in your context.
Even in this scenario it’s feasible for standards to change. ISBN-15 becomes a thing and suddenly you have books that never get an ISBN-13 so your primary key constraints cause an error for trying to insert a null. Granted, you can see a lot of these changes coming but again, they come on a schedule you don’t control.
These things can just be unique fields. I think the takeaway here is exactly to not use these unique fields as database keys if you have the option / if it’s up to you.
I don’t think that holds true in all scenarios. You need to use a key that has some guarantees. In many systems you will use data you don’t control, like email addresses, IBANs, ISBNs, passport IDs and many more. You have zero control over those keys, but because each comes with certain guarantees, they might be suitable as a foreign key in your context.
People regularly change email addresses. Listing that as an example is a particularly bad example in my opinion.
Even in this scenario it’s feasible for standards to change. ISBN-15 becomes a thing and suddenly you have books that never get an ISBN-13 so your primary key constraints cause an error for trying to insert a null. Granted, you can see a lot of these changes coming but again, they come on a schedule you don’t control.
These things can just be unique fields. I think the takeaway here is exactly to not use these unique fields as database keys if you have the option / if it’s up to you.