If you don't want to keep a database user any more, you should delete the user by using the "DROP USER" statement. This tutorial exercise shows how to delete "Dba_User":

-- Login with "sa"

USE GlobalGuideLineDatabase;

GO

DROP USER Dba_User;

GO

-- List all user names

SELECT name, sid, type, type_desc

FROM sys.database_principals WHERE type = 'S';

name    sid    type type_desc

-------------------- ------------------------ ---- ---------

dbo   0x01    S SQL_USER

guest   0x00    S SQL_USER

INFORMATION_SCHEMA NULL    S SQL_USER

sys   NULL    S SQL_USER

User "Dba_User" has been deleted now.