what is a trigger?

[susarlasireesha]

DDL tiggers are operate on Create, Drop,Alter and are useful to perform administrative tasks and enforce business rules.

DMl triggers are operate on Insert,Update,Delete and they are useful to enforce business rules and maintain data integrity when dml commands operate on tables(views).

[shobi_at]

A DML trigger is a stored procedure that goes into effect when you insert, delete, or update data in a table. You can use triggers to perform a number of automatic actions, such as cascading changes through related tables, enforcing column restrictions, comparing the results of data modifications, and maintaining the referential integrity of data across a database.

DML Triggers are automatic. They work no matter what caused the data modification. A trigger is specific to one or more of the data modification operations, update, insert, and delete and is executed once for each SQL statement.

For example, to prevent users from removing any publishing companies from the publishers table, you could use this trigger:


Thanks
Shobi