Sql Server User Mapping Error 15023

The Issue at Hand

Error 15023 is a manifestation of an orphaned user situation in SQL Server, occurring when the database user becomes unlinked from the corresponding server login.

Practical Workarounds

1. Duplicating Logins: the 'Clone Wars' 😉

A login not found? Fear not! Just create one with the correct SID:

CREATE LOGIN LoginName WITH PASSWORD = 'YourStrongPassword';  -- Use the force, choose a strong password.
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Map the UserName to LoginName:

ALTER USER UserName WITH LOGIN = LoginName;
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2. Auto-Repair: the SQL Server's 'Healing Touch' 👨‍⚕️

The Auto-Fix variant of sp_change_users_login is a cure for orphaned users:

EXEC sp_change_users_login 'Auto_Fix', 'UserName', 'LoginName', 'Password';  -- The good ol' 'doc' at work.
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This associates the orphaned user with an existent login. If LoginName is missing, it'll be created and the password reset.

3. Double Trouble: When Users Already Exist 🐱‍👤🐱‍👤

Error 15023 persists? Check if the user already exists:

IF EXISTS (SELECT * FROM sys.database_principals WHERE name = N'UserName') 
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Proceed accordingly: consider altering or dropping the user.

4. Spring Cleaning Your Users 🧹

Assert control by dropping and recreating:

DROP USER UserName; -- Say bye!
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Recreate the login & user - it's like a user's rebirth with everything reset!

5. Default Settings & Check of Territory 📌🌍

While altering user mappings, set the default schema:

ALTER USER UserName WITH DEFAULT_SCHEMA = schemaName;
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Always verify your database context:

USE DatabaseName;
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6. Preemptive Measures: Spy vs Spy 🕵️‍♂️

Before dropping users, check any potential role or permission disrupts.

Proactive Approaches

• SID Consistency: Ensure to maintain consistent SID values during migrations.
• Audit Regularly: Schedule routine checks for user-to-login mappings.
• Security First: When updating or creating new logins, remember ALTER LOGIN and adhere to strong password policies.
• Use of Scripts: Rely on scripts generated by SSMS when migrating users.