instead of and for Triggers

For example, an update statement on a view with an instead of update trigger causes the trigger to execute. If the trigger contains a SQL statement updating a table with a for trigger defined on it, that trigger fires. The for trigger may contain a SQL statement that updates another view with an instead of trigger that then executes, and so forth.

instead of and for triggers have different recursive behaviors. for triggers support recursion, while instead of triggers do not. If an instead of trigger references the same view on which the trigger was fired, the trigger is not called recursively. Rather, the triggering statement applies directly to the view; in other words, the statement is resolved as modifications against the base tables underlying the view. In this case, the view definition must meet all restrictions for an updatable view. If the view is not updatable, an error is raised.

For example, if a trigger is defined as an instead of update trigger for a view, the update statement executed against the same view within the instead of trigger does not cause the trigger to execute again. The update exercised by the trigger is processed against the view, as though the view did not have an instead of trigger. The columns changed by the update must be resolved to a single base table.