informix触发器（Informix flip-flop）.docVIP

informix触发器（Informix flip-flop） Informix triggers 1. Introduction Trigger (trigger) is a special procedure, it is not executed by the program, nor manual start, but by the event to be triggered, for example when operating on a table or view (insert, delete, update) will activate it to perform. Triggers are often used to strengthen data integrity, constraints, and business rules. Triggers can also be used to enforce referential integrity to preserve relationships defined between tables when they are added, updated, or deleted in multiple tables. However, the best way to enforce referential integrity is to define primary keys and foreign key constraints in the correlation table. If you use a database diagram, you can create relationships between tables to automatically create foreign key constraints. Operations in a trigger can be insert, update, delete, execute, procedure, or execute function operations. On a table or view, you can have multiple insert, update, select, or delete triggers. 2. Important concepts 1) trigger name Identifies a trigger and must remain unique in the database. 2) triggering events I) the database statement can start the trigger. Events that can be triggered are insert, update, delete, or select statements; (II) in update or select events, a multiple field is added as trigger when triggered; (III) in insert or delete events, any insert or delete operation on a table can trigger a trigger; IV) triggers are created in local tables or views. It cannot be created in a table or view of a remote database. 3) triggered action I) triggered actions refer to some SQL statements executed when an event is triggered; II) there are three types of trigger actions: before, after, and for each row; III) the before trigger action is performed before the trigger event occurs; IV) the after trigger action is executed after the trigger event occurs; V) the for each row trigger action affects all records that trigger the event to occur; VI) trigger actions can be