Question

Just talking about SQL Server auhentication, has a Login Name to be the same from the User Name?

Answer 1

No, the login name and user name do not have to be the same – you can create a different user name in each database, all based off the same server-level login.

USE master;
GO 

CREATE LOGIN foo WITH PASSWORD = 'bar', CHECK_POLICY = OFF;
GO

USE tempdb;
GO

CREATE USER blat FROM LOGIN [foo];
GO

That said, why would you want to do this? It’s completely confusing.