An ‘SQL Trigger’ is a compiled unit of SQL Server procedure, which can run automatically when an event occurs on the database objects. For example, you can write a piece of SQL Script (the trigger), which can be called whenever an insert (the event) takes place on a specific table. There are various types of triggers possible in SQL Server. The two crucial types are:
DDL Triggers: These triggers act on ‘Data Definition Language’; say, for example, a trigger procedure runs whenever a table is created. We can say DDL trigger as an ‘Database level trigger’ hence it acts on the DB. SQL Server invokes the Trigger procedure whenever the manipulation like Create, Alter and Drop takes place on its DB objects.
DML Triggers: These triggers act on ‘Data Manipulation Language’. In DB world, the tables maintain the Data. So, we can do manipulating data through the tables by making use of Insert, Update and Delete statements on the table. We can call DML trigger as an ‘Table Level Trigger’ since it operates at table level. Simply,