Triggers are special kind of stored procedures that get
executed automatically when an INSERT, UPDATE or DELETE operation takes place
on a table. . It can be used to maintain referential integrity. A trigger can call
stored procedure.
Triggers can't be invoked on demand. They get triggered
only when an associated action (INSERT, UPDATE, DELETE) happens on the table on
which they are defined. Triggers can also be used to extend the referential integrity checks. You
can specify which trigger fires first or fires last using sp_settriggerorder.
Triggers are generally used to implement business rules,
auditing. Triggers can also be used to extend the referential integrity checks,
but wherever possible, use constraints for this purpose, instead of triggers,
as constraints are much faster.