Elements of Triggers (in SQL3)
- Timing of action execution: before, after or instead of triggering
- The action can refer to both the old and new state of the database.
- Update events may specify a particular column or set of columns.
- A condition is specified with a WHEN clause.
- The action can be performed either for
- once for every tuple, or
- once for all the tuples that are changed by the database operation.