Trigger for gbase 8s

         trigger （Trigger） Is a special stored procedure . On the watch INSERT、DELETE or UPDATE In operation , Some triggers can be defined to make the database server automatically call stored procedures or SQL sentence . Triggers maintain the consistency of logically related data in different tables , Maintain the relevant integrity of the data .

         Triggers can also be used to enforce referential integrity , To add to multiple tables 、 When a row is updated or deleted , Retain the relationships defined between these tables . However , The best way to enforce referential integrity is to define primary and foreign key constraints in related tables . If you use a database diagram , You can create relationships between tables to automatically create foreign key constraints .

         Triggers are sometimes called events - Conditions - Action rules （Event-Condition-Action Role,ECA The rules ）.

A trigger consists of three parts :

（1） event ： It refers to the insertion into the database 、 Delete 、 Modification and other operations . When an event declared by the database programmer occurs , Trigger starts working .

（2） Conditions ： When the trigger is activated by an event , Not immediately , Instead, the trigger tests the trigger condition first . If the condition holds , Then the trigger executes the corresponding action , Otherwise the trigger does nothing .

（3） action ： If the trigger meets the predefined conditions , Then the action associated with the trigger （Action） Executed by the database management system . These actions can prevent events from happening （ I.e. cancellation event , For example, delete the tuple just inserted ）, It can be a series of database operations , It can even be related to other operations that have nothing to do with triggering events .