Discuss the strengths and weaknesses of the trigger mechanism. Con- trast triggers with other integrity constraints supported by SQL.

A trigger is a procedure that is automatically invoked in response to a specified change to the database. The advantages of the trigger mechanism include the ability to perform an action based on the result of a query condition. The set of actions that can be taken is a superset of the actions that integrity constraints can take (i.e. report an error). Actions can include invoking new update, delete, or insert queries, perform data definition statements to create new tables or views, or alter security policies. Triggers can also be executed before or after a change is made to the database (that is, use old or new data).

There are also disadvantages to triggers. These include the added complexity when trying to match database modifications to trigger events. Also, integrity constraints are incorporated into database performance optimization; it is more difficult for a database to perform automatic optimization with triggers. If database consistency is the primary goal, then integrity constraints offer the same power as triggers. Integrity constraints are often easier to understand than triggers.