> Except that: 1. Email actually works quite well as an individual identifier.

No, it doesn't.

> At any given time, an email account is probably linked to only one person.

Lots of people have shared email accounts. And even without that the "at any one time" is one reason why it doesn't work as an individual identifier, its not stable. (Since cell phones and number portability have become ubiquitous, phone numbers are probably better than email addresses at this, but share the same sorts of problems.)

> 2. No alternative exists, in real world use, that really looks better

Sure alternatives exist. While its often important to have a contact email address connected to an identity, there is no reason to have an externally-meaningful value that is inextricably tied to the online identity, particularly if that value doesn't have an intrinsic, unique, and stable link to a particular person.

You're justifying choosing a bad natural key with the argument that its the least-bad natural key, when not only is the proposition that the proposed key is the least-bad natural key somewhat dubious, more importantly, the use case calls for a key, but there is no reason for it to be a natural key.

«You're justifying choosing a bad natural key with the argument that its the least-bad natural key, when not only is the proposition that the proposed key is the least-bad natural key somewhat dubious, more importantly, the use case calls for a key, but there is no reason for it to be a natural key.»

Of course it has to be a natural key! Are you expecting that users will learn your theoretically perfect surrogate key? Do you understand that you will be competing for space in people's brain? For what reason? Because shared email accounts break the many to one relationship on mail <-> person?

> Of course it has to be a natural key! Are you expecting that users will learn your theoretically perfect surrogate key?

I'm not sure why users should ever need to know the key.

> Because shared email accounts break the many to one relationship on mail <-> person?

No, I probably wouldn't even both with addressing the problem of shared email accounts (which would require some discriminator), but with one person having multiple email accounts and email accounts changing over time. These things indicate that accounts should have transitory, one-to-many relationships to email addresses, rather than email addresses serving as a key.

«These things indicate that accounts should have transitory, one-to-many relationships to email addresses, rather than email addresses serving as a key.»

The only requirement for the email to be a key to the account is the association of one email to one person. A person can have more than one email, at different times or at the same time. The only thing that can't happen is one email mapping to two individuals. Full circle: the majority of emails do map to one individual and the cases where they do not map, are not enough to preclude the use of emails as keys.

Perhaps the confusion occurs because you think I'm defending email as a primary key for the account. I'm not. It's one key, not the primary key.