Trigger overview v16
A trigger is a named SPL code block that's associated with a table and stored in the database. When a specified event occurs on the associated table, the SPL code block executes. The trigger is said to be fired when the code block executes.
The event that causes a trigger to fire can be any combination of an insert, update, or deletion carried out on the table, either directly or indirectly. If the table is the object of a SQL
TRUNCATE command, the trigger is directly fired when the corresponding insert, update, delete, or truncate event is defined as a triggering event. The events that fire the trigger are defined in the
CREATE TRIGGER command.
A trigger can fire indirectly if a triggering event occurs on the table as a result of an event initiated on another table. For example, suppose a trigger is defined on a table containing a foreign key defined with the
ON DELETE CASCADE clause, and a row in the parent table is deleted. In this case, all children of the parent are deleted as well. If deletion is a triggering event on the child table, deleting the children causes the trigger to fire.