BANGALORE, INDIA: It has been more than two decades since Relational Database Management Systems (RDBMS) have made transition from the laboratory to becoming the data store of choice for all large and small businesses.
And with time, database servers are increasingly becoming sophisticated and are providing more functionalities and features to the developers, administrators and architects. It would benefit us a lot if we learn what new is coming new with each version.
In Microsoft SQL Server , the versions in use across development houses in India are primarily 2000 and 2005, and in a few cases, 2008. The move from Microsoft SQL Server 2000 to 2005 was a big leap with many new functionalities and features introduced. The concept of DDL Triggers was one such new feature.
We know about triggers as they exist in SQL Server 2000 and its previous versions ? triggers that fire in response to INSERT, UPDATE and DELETE events. They are now called as DML triggers, as they fire in response to DML events. The new triggers that we are discussing now fire in response to DDL events, for example CREATE TABLE. Hence they are called DDL triggers. The code samples presented here run on an instance of SQL Server 2008, but they would also run on SQL Server 2005 also.
Before we get into serious business usage, I would demonstrate a simple DDL trigger that displays a message in response to the CREATE TABLE event.
CREATE TRIGGER DDLDemo
ON DATABASE
FOR CREATE_TABLE
AS
PRINT 'Table Created!'
After the trigger has been created at the database level, let us now create a table and see if the trigger is getting executed.
CREATE TABLE employee
(
EmployeeID int primary key,
EmployeeName nvarchar(30)
)
As you can see, the trigger gets fired in response to any create table statement.
EVENTDATA
If you have used DML triggers extensively you would know there would be times when you need to know which rows are being inserted, updated or deleted; what are the old values and what are the new values. In DML triggers, we use the magic tables inserted and deleted to answer these queries.
In DDL triggers you would need to know what is the activity that is being carried out, who is carrying it out the activity, when is the activity being carried out, what is the query that is being executed, and so on.
The EVENTDATA() function answers these questions when fired from within a trigger.
