A trigger is a special kind of stored procedure that goes into effect when you modify data in a specified table using one or more data modification operations: UPDATE, INSERT, or DELETE. Triggers can query other tables and can include complex SQL statements. They are primarily useful for enforcing complex business rules or requirements. For example, you could control whether to allow an order to be inserted based on a customer's current account status.
Triggers are also useful for enforcing referential integrity, which preserves the defined relationships between tables when you add, update, or delete the rows in those tables. However, the best way to enforce referential integrity is to define primary key and foreign key constraints in the related tables. If you use database diagrams, you can create a relationship between tables to automatically create a foreign key constraint. For details, see Table Relationships.
Triggers are useful in these ways:
title_id
column of the titles
table to cause a deletion of matching rows in other tables. The trigger uses the title_id
column as a unique key to locate matching rows in the titleauthor
, sales
, and roysched
tables.discounts
table) to books (stored in the titles
table) with a price of less than $10.For details about working with triggers, see the following topics:
To | See |
Create new triggers | Creating a Trigger |
Open existing triggers | Opening a Trigger |
Save triggers to your project | Saving a Trigger |
Change the name of a trigger | Renaming a Trigger |
Delete stored triggers | Deleting a Trigger |