SQL Server Triggers

The sixtieth and final part of the SQL Server Programming Fundamentals tutorial considers the use of triggers. SQL Server triggers can be defined against tables and views to intercept insert, update and delete statements and modify their results.

What are Triggers?

Triggers are a special type of stored procedure. Instead of being executed manually, they run automatically in response to events that occur in a database. In this article we will examine triggers that run when data is inserted, updated or deleted. There are other types of trigger supported by SQL Server 2005 that allow actions to be performed when the schema of a database is changed or when a user logs on. These are beyond the scope of this tutorial.

Triggers are often used to audit changes to data by recording when modifications are made and, optionally, the previous version of the information. They are also used to enforce business rules and data integrity when those rules are too complex to be controlled by primary keys, foreign keys, unique constraints or check constraints. In such cases, rules may be checked and, if broken, data changes can be disallowed, transactions can be rolled back and errors may be raised.

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