System administrator (sa) is a special login. By default, it is assigned to the sysadmin fixed server role and cannot be changed. It is provided for backward compatibility with earlier versions of Microsoft® SQL Server™. Although sa is a built-in administrator login, it should not be used routinely. Instead, system administrators should be made members of the sysadmin fixed server role, and log on using their own logins instead. Use sa only when there is no other way to log in to SQL Server; for example, when other system administrators are unavailable, or have forgotten their passwords.
Note When SQL Server is installed, the sa login is not assigned a password. It is recommended that the password be assigned immediately to prevent unauthorized access to SQL Server using the sa login.