> Like usernames. You don’t use usernames as primary keys for anything, do you? What happens when people marry? well it's extremly painful to rename the primar

> Like usernames. You don’t use usernames as primary keys for anything, do you? What happens when people marry? well it's extremly painful to rename the primary mail address or the UPN when it comes to microsoft 365 and active directory, especially in a hybrid environment. of course you can change upn's but it's definitly some kind of "primary key" for a user. in fact most systems at least use a UPN