What Is a Trigger?

A trigger is a specialized stored procedure that will be executed either on a data modification, known as a Data Manipulation Language (DML) trigger, or on a data model action, such as CREATE TABLE, known as a Data Definition Language (DDL) trigger. DML triggers are pieces of code attached to a specific table that are set to automatically run in response to an INSERT, DELETE, or UPDATE command. However, a DDL trigger is attached to an action that occurs either within a database or within a server. The first part of the chapter will look at DML triggers, followed by an investigation of DDL triggers. As a developer, you will use DML triggers mainly, and you will find DDL triggers used mainly by database administrators to ensure that certain actions cannot happen or are reported.