How To Use A Trigger In Database?

A trigger is an object contained within an SQL Server database that is used to execute a batch of SQL code whenever a specific event occurs. As the name suggests, a trigger is “fired” whenever an INSERT, UPDATE, or DELETE SQL command is executed against a specific table.

Triggers are associated with a single table, and are automatically executed internally by SQL Server.

Triggers are a powerful tool that can be used to enforce the business rules automatically when the data is modified. Triggers can also be used to maintain the data integrity. But they are not to maintain data integrity. Triggers should be used to maintain the data integrity only if you are unable to enforce the data integrity using CONSTRAINTS, RULES and DEFAULTS. Triggers cannot be created on the temporary tables.

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A trigger is a database object that is attached to a table. In many aspects it is similar to a stored procedure. As a matter of fact, triggers are often referred to as a "special kind of stored procedure." The main difference between a trigger and a stored procedure is that the former is attached to a table and is only fired when an INSERT, UPDATE or DELETE occurs. You specify the modification action(s) that fire the trigger when it is created.

When to Use Triggers

There are many reasons to use triggers. If you have a table which keeps a log of messages, you may want to have a copy of them mailed to you if they are urgent. If there were no triggers you would have some solutions, though they are not as elegant. You could modify the application(s) logging the messages. This means that you might be redundantly coding the same thing in every application that logs messages.

Tables can have multiple triggers. The CREATE TRIGGER statement can be defined with the FOR UPDATE, FOR INSERT, or FOR DELETE clauses to target a trigger to a specific class of data modification actions. When FOR UPDATE is specified, the IF UPDATE (column_name) clause can be used to target a trigger to updates affecting a particular column.

SQL Server 2000 greatly enhances trigger functionality, extending the capabilities of the triggers you already know and love, and adding a whole new type of trigger, the "Instead Of" trigger.

SQL Server 2000 has many types of triggers:

1. After Trigger

2. Multiple After Triggers

3. Instead Of Triggers

4. Mixing Triggers Type