18. Triggers

At times a modification to data somewhere within your database will require an automatic action on data elsewhere, either in your database, another database, or elsewhere within SQL Server; a trigger is the object that will do this for you. When a modification to your data occurs, SQL Server will fire a trigger, which is a specialized stored procedure that will run, performing the actions that you desire. Triggers are most commonly used to perform business rules validation, carry out cascading data modifications (changes on one table causing changes to be made on other tables), and keep track of changes for each record (audit trail). You can also do any other processing that you require when data on a specific table are modified, such as auditing. You actually have come across triggers when looking at Declarative Management Framework earlier in the book in Chapter 3. These specialized system triggers are built to ensure the system’s integrity. You will see how these work by building your own DDL trigger later in this chapter.