Find and Fix Orphaned Users in SQL Server

Last updated: August 28, 2026.

A database user can remain after its server login is missing or has a different SID. This often appears after restoring a database on another instance.

Report and repair the mapping

USE YourDatabase;
GO
SELECT dp.name AS DatabaseUser, dp.sid
FROM sys.database_principals AS dp
LEFT JOIN sys.server_principals AS sp ON dp.sid = sp.sid
WHERE dp.authentication_type_desc = 'INSTANCE'
  AND dp.type IN ('S','U','G')
  AND sp.sid IS NULL;
GO
ALTER USER [AppUser] WITH LOGIN = [AppLogin];

Verify before changing

• Confirm that the login represents the same identity.
• Create the login first when it is truly missing.
• Review role membership and explicit grants.
• Test application access with least privilege.

Reference: Microsoft ALTER USER documentation.