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A trigger on the table can ensure the proper format of all data added to it.
Because the trigger executes whenever any client adds data to the table, no client can circumvent the rules, and the code that enforces the rules can be stored and maintained only in the trigger, rather than in every client application.
You might be unaware that a trigger is executing unless it causes an error that is not handled properly. A trigger defined on a schema fires for each event associated with the owner of the schema (the current user).
A trigger defined on a database fires for each event associated with all users.
Unlike a subprogram, a trigger cannot be invoked directly.
A trigger is invoked only by its triggering event, which can be caused by any user or application.
A trigger can have the same name as another kind of object in the schema (for example, a table); however, Oracle recommends using a naming convention that avoids confusion. By default, a trigger is created in the enabled state.
You can disable an enabled trigger, and enable a disabled trigger.
Constraint behavior depends on constraint state, as explained in .Constraints are easier to write and less error-prone than triggers that enforce the same rules.However, triggers can enforce some complex business rules that constraints cannot.While a trigger is , which determines whether the trigger fires before or after the triggering statement runs and whether it fires for each row that the triggering statement affects. If the trigger is created on a schema or the database, then the triggering event is composed of either DDL or database operation statements, and the trigger is called a )".By default, a trigger is created in the enabled state. When a trigger fires, tables that the trigger references might be undergoing changes made by SQL statements in other users' transactions.
SQL statements running in triggers follow the same rules that standalone SQL statements do.