Logon failed due to trigger execution

 The error "Logon failed due to trigger execution" occurs when a logon trigger in SQL Server prevents a user from logging in. Logon triggers are special stored procedures that execute in response to a LOGON event, and they can be used to enforce security policies, restrict access, or log login activity.

Steps to Resolve the Issue

1. Identify the Logon Trigger:

• Determine which logon trigger is causing the issue by querying the system catalog.

SELECT name, create_date, modify_date, is_disabled
FROM sys.server_triggers
WHERE type = 'TR' AND parent_class_desc = 'SERVER';

Check the Trigger Definition:

• Check the code of the logon trigger to understand its logic and why it might be causing the logon to fail.

-- Check the trigger defination
EXEC sp_helptext 'TriggerName';

Disable the Trigger (If Appropriate):

• If the trigger is incorrectly preventing logons, you can disable it.

-- Disable the trigger
DISABLE TRIGGER TriggerName ON ALL SERVER;

Fix the Trigger Logic (If Needed):

• If the trigger logic needs adjustment, modify the trigger code accordingly.

ALTER TRIGGER TriggerName ON ALL SERVER
FOR LOGON
AS
BEGIN
    -- Your trigger logic here
END;

Re-enable the Trigger:

• After fixing the issue, re-enable the trigger.

ENABLE TRIGGER TriggerName ON ALL SERVER;

Example Scenario and Solutions

Scenario: A Logon Trigger Prevents All Logins

Problematic Trigger:

CREATE TRIGGER PreventLogons
ON ALL SERVER
FOR LOGON
AS
BEGIN
    ROLLBACK;
END;

This trigger prevents all logons by rolling back every login attempt.

Solution:

1. Disable the Trigger:

DISABLE TRIGGER PreventLogons ON ALL SERVER;

Modify the Trigger Logic (e.g., to allow logins during business hours):

ALTER TRIGGER PreventLogons ON ALL SERVER
FOR LOGON
AS
BEGIN
    IF DATEPART(HOUR, GETDATE()) NOT BETWEEN 9 AND 17
    BEGIN
        ROLLBACK;
    END;
END;

Re-enable the Trigger:

ENABLE TRIGGER PreventLogons ON ALL SERVER;

Practical Steps to Diagnose and Fix the Issue

1. Identify Active Logon Triggers:

SELECT name, create_date, modify_date, is_disabled
FROM sys.server_triggers
WHERE type = 'TR' AND parent_class_desc = 'SERVER';

Review Trigger Definition:

-- Replace 'TriggerName' with the name of the trigger
EXEC sp_helptext 'TriggerName';

Disable the Trigger:

-- Replace 'TriggerName' with the name of the trigger
DISABLE TRIGGER TriggerName ON ALL SERVER;

Fix or Adjust the Trigger Logic:

ALTER TRIGGER TriggerName ON ALL SERVER
FOR LOGON
AS
BEGIN
    -- Adjust the logic to prevent inappropriate logon failures
END;

Re-enable the Trigger:

ENABLE TRIGGER TriggerName ON ALL SERVER;

By following these steps, you can diagnose and resolve issues related to logon triggers preventing successful logins

User or role already exists in the current database

 The error "User or role already exists in the current database" occurs when you try to create a user or role that already exists in the database. Here are steps to resolve this issue:

Steps to Resolve

1. Check Existing Users or Roles:

• Verify if the user or role already exists in the database

-- Check if the user exists
SELECT name 
FROM sys.database_principals 
WHERE type IN ('U', 'S') AND name = 'YourUserName';

-- Check if the role exists
SELECT name 
FROM sys.database_principals 
WHERE type = 'R' AND name = 'YourRoleName';

Drop the Existing User or Role (If Appropriate):

• If it’s safe to do so, you can drop the existing user or role before creating a new one

-- Drop the existing user
DROP USER [YourUserName];

-- Drop the existing role
DROP ROLE [YourRoleName];

Create the User or Role:

• Now, you can create the user or role without encountering the error.

-- Create a new user
CREATE USER [YourUserName] FOR LOGIN [YourLoginName];

-- Create a new role
CREATE ROLE [YourRoleName];

Example Scenarios and Solutions:

Scenario 1: Creating a User

Problematic Query:

CREATE USER [MyUser] FOR LOGIN [MyLogin];

Error Message:

User or role 'MyUser' already exists in the current database.

Solution:

Check if the user exists:

SELECT name 
FROM sys.database_principals 
WHERE type IN ('U', 'S') AND name = 'MyUser';

Drop the user if it exists (if appropriate):

DROP USER [MyUser];

Create the user:

CREATE USER [MyUser] FOR LOGIN [MyLogin];

Scenario 2: Creating a Role

Problematic Query:

CREATE ROLE [MyRole];

Error Message:

User or role 'MyRole' already exists in the current database.

Solution:

1. Check if the role exists:

SELECT name 
FROM sys.database_principals 
WHERE type = 'R' AND name = 'MyRole';

Drop the role if it exists (if appropriate):

DROP ROLE [MyRole];

Create the role:

CREATE ROLE [MyRole];

Handling the Issue Without Dropping:

If you do not want to drop the existing user or role (for instance, to preserve permissions or dependencies), you can skip creation if it already exists. Here’s how:

Creating a User Only If It Doesn't Exist

IF NOT EXISTS (SELECT * FROM sys.database_principals WHERE type IN ('U', 'S') AND name = 'MyUser')
BEGIN
    CREATE USER [MyUser] FOR LOGIN [MyLogin];
END;

Creating a Role Only If It Doesn't Exist:

IF NOT EXISTS (SELECT * FROM sys.database_principals WHERE type = 'R' AND name = 'MyRole')
BEGIN
    CREATE ROLE [MyRole];
END;

By following these steps, you can handle the "User or role already exists in the current database" error effectively.