DML triggers are invoked when a DML event occurs in the database. DML events manipulate or modify the data in a table or view. These events include insertions, updates, and deletions.
DML triggers are powerful objects for maintaining database integrity and consistency. They are able to evaluate data before it has been committed to the database. During this evaluation period, these triggers can perform a myriad of actions, including the following:
Compare before and after versions of data.
Roll back invalid modifications.