You name a trigger in the CREATE TRIGGER statement. A trigger
    name must be unique within a schema of a multischema database or
    unique within a nonmultischema database.

    A trigger defines the actions to occur before or after a
    specified table is updated (by a write operation such as an
    INSERT, DELETE, or UPDATE statement). A trigger can be thought
    of as a rule on a single table, which takes effect at a specific
    time for a particular type of update and causes one or more
    triggered actions to be performed.

    With triggers, you can define useful actions such as:

    o  Cascading deletes

       Deleting a row from one table causes additional rows to be
       deleted from other tables that are related to the first table
       by key values.

    o  Cascading updates

       Updating a row in one table causes additional rows to be
       updated in other tables that are related to the first table
       by key values. These updates are usually limited to the key
       values themselves.

    o  Summation updates

       Updating a row from one table causes a value in a row of
       another table to be updated by being increased or decreased.

    o  Hidden deletes

       Causing rows to be deleted from a table by moving them to a
       parallel table that is not used by the database.

    o  Audit log

       Records when and by whom a row is inserted, updated, or
       deleted.