Questions about User Name/Alias Storage

Recently I realized that using a "first and last" name as the custom field type might be in my best interest for the project I'm working on. So I decided to change the option to use first and last instead of the single name option. From an administrator point of view things are working almost perfectly as expected (quite flexible too).

But I am questioning the storage procedure, or at least trying to understand how it works. When I change the first or the last name it updates the _users table. Are these values also stored else where? If I put in the first name "Josh Lewis" it stores it in the _users table as "Josh Lewis". If I put in the first name "Josh" and last name "Lewis" it stores it the same in the _users table. But how could ES possibly know they are separate names unless this data is being stored somewhere else? Editing my profile proves that ES keeps them separated, or at least visually. My point is that I suspect it's being stored else where to store the separated names. But I cannot find where (if there is any).

While I'm on the subject of names/tables, I also want to chat about alias's. The database table _social_users has an alias column which appears to store the same values as the username column from _users. Isn't this duplicate data? Or is a foreign key being used?

I'm just trying to make sure the best practices are being used. Perhaps they already are? My curious mind is trying to make sure of this. Hope all is well for the stacked team.