AFTER triggers

Triggers that run after an update, insert, or delete can be used in several ways.

Triggers can update, insert, or delete data in the same or other tables. This is useful to maintain relationships between data or to keep audit trail information.
Triggers can check data against values of data in the rest of the table or in other tables. This is useful when you cannot use referential integrity constraints or check constraints because of references to data from other rows from this or other tables.
Triggers can use user-defined functions to activate non-database operations. This is useful, for example, for issuing alerts or updating information outside the database.

Example

The following example presents an AFTER trigger that increases the number of employees when a new employee is hired.


    CREATE TRIGGER NEW_HIRE
      AFTER INSERT ON EMPLOYEE
      FOR EACH ROW
      UPDATE COMPANY_STATS SET NBEMP = NBEMP + 1