Well, Trigger was the name of Roy Rogers' horse, but in the Oracle world, a trigger is an important system-level component that allows you to associate a hunk of code (usually PL/SQL or Java) with a specific system event, namely DML (SQL insert, update and delete) statements.nstead-of triggers are used when views are involved, and are a good way of avoiding the mutating table trigger-related error. Database event triggers can be divided into two categories: on the database, where triggers occur for all users, and on a schema, where triggers occur for that user.