Oracle Security

Table Triggers

A trigger is a special stored program attached to a table. A trigger is executed when the event on which it is based occurs. There is a distinct difference between triggers and other types of stored programs. A trigger is directly associated with a table and always includes the event for which an action will occur. Since execution, or “firing of the trigger,” is controlled only by this event, triggers cannot be executed directly by a user. In contrast, stored programs can be executed directly by an authorized user.

A trigger cannot be created unless the text of the command includes a table name. Consequently, if the table is dropped, the trigger will also be dropped automatically.

About Creating a Trigger

The statement that creates a trigger includes both the triggering event and the table name. You can specify that a trigger is to be fired either before or after the event, followed by one or more actions such as INSERT, UPDATE, or DELETE. Within Oracle8, you can also specify the INSTEAD OF condition. That is used to solve the problem of updating through complex views. All triggers are based on modification events. Triggers can be quite useful from a security standpoint to track or prevent activities that change the data.

For security and/or monitoring purposes, tables are frequently created with extra fields to capture the username, time, and modification action performed. These additional columns are intended to be used for auditing. However, such a scheme only retains ...