SQL SERVER – 2005 – Server and Database Level DDL Triggers Examples and Explanation

I was asked following questions when discussing security issues in meeting with off-shore team of large database consultancy company few days ago. I will only discuss one of the security issue was discussed accidental data modification by developers and DBAs themselves.

How to alter modification in database by system admin himself?

How to prevent accidents due to fat fingers? (Accidental execution of code)

How to display message to contact another developers when another developer tries to modify object another developer working on?

It was interesting conversation. Answer to all the questions is correct assignment of permissions and (when permissions are not an issue) Server and Database Level DDL Triggers. If developers have their own login to SQL Server and it does not have permissions to drop or create objects this will not be issue at all. However, there are still risk of System Admin himself making accidental mistakes. The solution to this will be use Server and Database Level DDL Triggers.

DDL is abbreviation of Data Definition Level. DDL contains schema of the database object. It was always dream of all DBA, when change in mission critical schema of the database or server is attempted it is prevented immediately informing DBA and users automatically. DDL Trigger can now make this dream true. Definition of DDL Trigger (from BOL) is DDL Triggers are a special kind of trigger that fire in response to Data Definition Language (DDL) statements. They can be used to perform administrative tasks in the database such as auditing and regulating database operations.

DML is abbreviation of Data Manipulation Level. DML contains the actual data which is stored in the database schema. UPDATE, INSERT, DELETE, SELECT are clause are used to manipulate database. There is following different between DML and DDL triggers.

• DDL triggers do not support INSTEAD OF feature DML triggers.
• DDL triggers do not have feature of inserted and deleted tables like DML triggers as it does not participate in database manipulations.

Following example demonstrates how DDL trigger can be used to prevent dropping stored procedure.

Step 1 :

First create any sample stored procedure.
USE AdventureWorks; 
GO 
CREATE PROCEDURE TestSP             
AS 
SELECT 1 test; 
GO 

Step 2 :

Create DDL trigger which will prevent dropping the stored procedure.

USE AdventureWorks 
GO 
CREATE TRIGGER PreventDropSP             
ON DATABASE             
FOR DROP_PROCEDURE             
AS
PRINT 'Dropping Procedure is not allowed. DDL Trigger is preventing this from happening. To drop stored procedure run following script. 
Script : DISABLE TRIGGER PreventDropSP ON DATABASE; <Run your DROP SP>; ENABLE TRIGGER PreventDropSP ON DATABASE;' 
ROLLBACK; 
GO 

Step 3 :

Now test above trigger by attempting to drop the stored procedure.

USE AdventureWorks 
GO 
DROP PROCEDURE TestSP; 
GO 

This should throw following message along with error code 3609 :

Dropping Procedure is not allowed.

DDL Trigger is preventing this from happening.

To drop stored procedure run following script.

Script :

DISABLE TRIGGER PreventDropSP ON DATABASE;

<Run your DROP SP>;

ENABLE TRIGGER PreventDropSP ON DATABASE;

Msg 3609, Level 16, State 2, Line 1

The transaction ended in the trigger. The batch has been aborted.

Step 4 :

Now DISABLE above trigger and it will let you successfully drop the stored procedure previously attempted to drop. Once it is dropped enable trigger again to prevent future accidents.

USE AdventureWorks 
GO             
DISABLE TRIGGER PreventDropSP ON DATABASE;
DROP PROCEDURE TestSP;
ENABLE TRIGGER PreventDropSP ON DATABASE; 
GO 

List of all the DDL events (DROP_PROCEDURE in example above) to use with DDL Trigger are listed on MSDN.