(For sometime after Wednesday:) Should we add an auto-increment integer column to be the primary key for the Users table (and the foreign key for all references to Users), and make the usernames column (that is currently the primary key) merely unique and non-null? Upside is it becomes way easier to change a username; downside is it would require a SQL JOIN any time someone wants to view a username related to a Message/MessageSetting/ConversationSetting/etc. (though not too hard).
(For sometime after Wednesday:) Should we add an auto-increment integer column to be the primary key for the Users table (and the foreign key for all references to Users), and make the usernames column (that is currently the primary key) merely unique and non-null? Upside is it becomes way easier to change a username; downside is it would require a SQL JOIN any time someone wants to view a username related to a Message/MessageSetting/ConversationSetting/etc. (though not too hard).