Assign a login to a user created without login (SQL Server)

Solution 1:

sp_change_users_login is deprecated.

Much easier is:

ALTER USER usr1 WITH LOGIN = login1;

Solution 2:

I found that this question was still relevant but not clearly answered in my case.

Using SQL Server 2012 with an orphaned SQL_USER this was the fix;

USE databasename                      -- The database I had recently attached
EXEC sp_change_users_login 'Report'   -- Display orphaned users
EXEC sp_change_users_login 'Auto_Fix', 'UserName', NULL, 'Password'