instead of Triggers

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. SAP ASE 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.

• Inserted and Deleted Logical Tables
  Deleted and inserted tables are logical (conceptual) tables. An inserted table is a pseudo-table containing rows with the inserted values of an insert statement, and a deleted table is a pseudo-table containing rows with the updated values (after image) of an update statement.
• Triggers and Transactions
  Both rollback trigger and rollback transaction are used for instead of triggers. rollback trigger rolls back the work done in any and all nested instead of triggers fired by the triggering statement. rollback transaction rolls back the work done in the entire transaction, up to the most recent savepoint.
• Nesting
  Like for triggers, you can nest instead of triggers to 16 levels. The current nesting level is stored in @@nestlevel.
• Recursion
  instead of and for triggers have different recursive behaviors.
• instead of insert Triggers
  You can define instead of insert triggers on a view to replace the standard action of the insert statement. Usually, this trigger is defined on a view to insert data into one or more base tables.
• instead of update Trigger
  Usually, the instead of update trigger is defined on a view, to modify data in one or more base tables.
• instead of delete Trigger
  instead of delete triggers can replace the standard action of a delete statement. Usually, an instead of delete trigger is defined on a view to modify data in base tables.
• Searched and Positioned update and delete
  You can search or position update and delete statements.
• Get Information About instead of Triggers
  Information about instead of triggers is stored as it is for for triggers.