One common issue that database administrators often run into is the old, familiar “orphaned” user problem. This happens when you use SQL Server Authentication to create a SQL Server login on your database server. When you do this, SQL Server generates a unique SID for that SQL Server login. After you create the SQL Server login, you typically create a database user in a user database on that server instance, and associate the database user with that SQL Server login.

This works fine until you try to restore that user database to another SQL Server instance. If you previously created a SQL Server login with the same UserID on the new server, the SID for that SQL Server login will not match the database user in the user database that you have restored (from the other database instance). Hence the term “orphaned” user.  This is an especially big issue if you are using database mirroring, since your database users will be orphans when you failover from one instance to the other instance. It is also an issue with log shipping, and it often comes up when you migrate from an old database server to a new database server.

There are several ways to fix this, but the best thing (outside of just using Windows Authentication and avoiding the problem), is to create the new server login using the same SID as on the original server. Just like you see below:

-- Get Sids for all SQL Server logins on the old server instance
SELECT name, [sid] 
FROM sys.server_principals
WHERE [type] = 's'; 

-- Create new SQL Login on new server instance
IF  EXISTS (SELECT * FROM sys.server_principals WHERE name = N'SQLAppUser')

-- Use the sid from the old server instance 
CREATE LOGIN SQLAppUser WITH PASSWORD = N'YourStrongPassword#', sid = 0x2F5B769F543973419BCEF78DE9FC1A64,