3.5. Triggers

v1.0.0 Summary Chapter 3: Database objects 3. Introduction 3.5. Triggers

Triggers are objects associated with a table that are used to execute operations stored in special functions when some operation (or event) happens on a single row or over the entire table. The trigger can be activated before or after the following events: INSERT, DELETE, UPDATE, or TRUNCATE. There is still a special behavior of a trigger that makes it able to execute the associated procedure instead of a certain event, this kind of trigger is known as constraint trigger.

Attribute	Description
`Type`	The type of trigger that is being configured. Possible values are `Ordinary trigger` and `Constraint trigger`. Extra attributes are enabled when configuring constraint triggers.
`Events`	Set of events when the trigger should be executed.
`Execution`	The moment when the trigger must be fired. Possible values are `BEFORE`, `AFTER`, and `INSTEAD OF` (this value is available only for constraint triggers).
`FOR EACH ROW`	The trigger must be executed each time a row changes.
`Function`	Function that will be executed when the trigger is fired. The function must return `trigger` and take no argument.
`Transition table names`	Defines custom names for the transition tables (relations) `OLD` and `NEW` during the trigger execution.
`Arguments`	A set of literal arguments optionally passed to the trigger at runtime. These arguments must be treated inside the trigger's function.
`Columns`	List of columns of the trigger's owner table that will cause the trigger to be activated in case of an `UPDATE` on those columns. If the trigger is configured with `INSTEAD OF` it can't be used with a list of columns.
`Constraint`	This tab handles the constraint trigger attributes. Constraint triggers work like a regular triggers but they can have the firing time adjusted through the command SET CONSTRAINTS.
`Deferrable`	Indicates if the constraint trigger can be deferred or not. The deferral mode is configurable only when this option is checked and the accepted values are `INITIALLY IMMEDIATE` and `INITIALLY DEFERRED`.
`Referenced Table`	Table referenced by the constraint trigger.
`Condition`	A boolean expression that determines when the trigger function will actually be executed.