duplicate usernames across multiple NAS that belong to different users

[Jonathan Davis]

E.g.

User1 on NAS1 has the username "user45"

User2 on NAS2 has the same username "user45"

We're using Yubikeys and SQL for 2FA/MFA, and I've got the Yubikey 
mappings sorted based in the clients.conf for each NAS

For SQL I can see multiple ways of doing this.

Add something (e.g NAS shortname) to the supplied username to match 
unique usernames in SQL

Use different SQL dbs for each NAS or Virtual Server (not a fan of this 
but it is an option)

Write some custom SQL queries and tables so that usernames are linked to 
groups via an index instead of usernames, this wouldn't be hard but not 
don't know if different SQL servers can use different SQL queries (Is it 
as simple as changing which query.conf to import?).

Being new, I don't know which option will lead us into FreeRadius hell, 
or if it doesn't really matter.

Thank you