If i understand the article correctly it's discussing using natural keys as primary keys. Eg if you're using login_name as a natural key then that's presumably replacing a more traditional user_id. So it would be hard not to use login_name as a foreign key in that scenario.

Where as if you still had a user_id as your primary key, you could still have user_id as a unique key (most RDBMS I've used support "unique keys") to enable the business logic discussed but without encouraging it's usage as a foreign key.

I think the article did touch on the fact that you can have multiple keys, but given it's heavy emphasis on finding natural keys over the more traditional logic of incremental integers, I can only assume the point of it wasn't about additional unique keys but rather alternatives for primary keys.

> If i understand the article correctly it's discussing using natural keys as primary keys.

I'm not sure about the author's intent here. In the prior section they dismiss the necessity of primary keys. However, the author rails on about unique keys. I'm not familiar with PostgreSQL, but I assume every reference to "key" is effectively an index with a unique constraint. If that is true then all of the discussed issues with unique names are the same even if the author doesn't care about primary key in particular.

From how I understand it the author does not make any suggestions to use natural keys as primary key. He just defines what is natural key. And he does mention that they may change and it has to be considered.

Actually in the summary he suggests to create column with uuid in each table and use it as primary key.

I agree, I can't think of any system off the top of my head that lets you change your handle, or why you would really want to. If it's a forum or has commenting capabilities, your handle is your absolute identity. If it's not a forum, no one ever really sees your username, so there's little motivation to change it.

> I can't think of any system off the top of my head that lets you change your handle, or why you would really want to.

Pretty much any system with a real name policy both does and needs to let you change your handle, because preferred real (and legal) names change. Now, these systems often use email addresses as login names, but they sometimes also support changing the primary email address as well. In effect, identity is most likely managed by a surrogate key that isn't exposed.

Twitter does (though I don't know of anyone who has). As does Google and Facebook. Github too.

Away from web services, gaming platforms like Nintendo's Switch allow for user name changes. As does the more enterprisey databases like ActiveDirectory (Windows logins), ldap and Linuxes / Unix passwd table also allows for login name changes.

To be honest, I've encountered more systems that do let you change your user name than systems that don't.

Stack Overflow lets you change your name.

eBay allows this. It's useful for brand management.

if you are linking the login name to other tables, author of a forum/board post, it gets complicated, after the login name changed...