instead of triggers are special stored procedures that override the default action of a triggering statement (insert, update, and delete), and perform user-defined actions.
The instead of trigger, like the for trigger, executes each time a data modification statement executes on a specific view. A for trigger fires after an insert/update/delete statement on a table, and is sometimes called an after trigger. A single instead of trigger can apply to one specific triggering action:
instead of update
It can also apply to multiple actions, in which the same trigger executes all the actions listed:
instead of insert,update,delete
Like for triggers, instead of triggers use the logical inserted and deleted tables to store modified records while the trigger is active. Each column in these tables maps directly to a column in the base view referenced in the trigger. For example, if a view named V1 contains columns named C1, C2, C3, and C4, the inserted and deleted tables contain the values for all four columns, even if the trigger modifies only columns C1 and C3. Adaptive Server automatically creates and manages the inserted and deleted tables as memory-resident objects.
instead of triggers allow views to support updates, and allow implementation of code logic that requires rejecting parts of a batch, while allowing other parts to succeed.
An instead of trigger is fired only once per data modification statement. A complex query containing a while loop may repeat an update or insert statement many times, firing the instead of trigger each time.
