How to make a Trigger when all you have are Events and Notifications
As usual, some of the best questions come from the newsgroups. And yet again, there was one that piqued by attention. The question essentially boiled down to “can you put a trigger on a login?” That is, the questioner wanted to execute some arbitrary T-SQL code whenever a user logged into a given instance of SQL Server. I’m not sure how you’d go about doing this in SQL Server 2000, but in 2005, two features make this possible – if you don’t mind building a bit of your own plumbing. These features are EVENT NOTIFICATIONS and the Service Broker.
Event Notifications are essentially fixtures that your create – using T-SQL – that allows SQL Server to dispatch messages about system events like logins, data definition language statements, and some trace events to Service Broker Services and Queues. The Service Broker Service acts as an address for the messages, while the Queue holds the messages until some a process like a Stored Procedure process them. Some number of instances of that Stored Procedure will be spawned by a process called Activation when a message arrives in a Queue. So these two features work together to deliver information about system events to a stored procedure that gets executed in response to that event, much like how a trigger gets fired in response to events.
What started out as fairly short post turned into a fairly long item, so I've contued this over here, while the annotated source code (with bonus features) is over here.