SQL$HELP72.HLB  —  CREATE  TRIGGER
    Creates triggers for a specified table. A trigger defines the
    actions to occur before or after the table is updated (by a write
    operation such as an INSERT, DELETE, or UPDATE statement). The
    trigger is associated with a single table, takes effect at a
    specific time for a particular type of update, and causes one or
    more triggered actions to be performed. If the trigger specifies
    multiple actions, each action is performed in the order in which
    it appears within the trigger definition.

    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 commonly limited to the key
       fields 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 otherwise used by the database.

                                   NOTE

       Combinations of table-specific constraints and appropriately
       defined triggers, by themselves, are not sufficient to
       guarantee that database integrity is preserved when the
       database is updated. If integrity is to be preserved,
       table-specific constraints and triggers must be used in
       conjunction with a common set of update procedures that
       ensure completely reproducible and consistent retrieval and
       update strategies.

    The CREATE TRIGGER statement adds the trigger definition to the
    physical database.

    A triggered action consists of an optional predicate and some
    triggered statements. If specified, the predicate must evaluate
    to true for the triggered statements in the action to execute.
    Each triggered statement is executed in the order in which it
    appears within the triggered action clause.

    The triggered statement can be:

    o  A DELETE statement

    o  An UPDATE statement

    o  An INSERT statement

    o  A CALL statement

    o  A SIGNAL statement

    o  A TRACE statement

    o  An ERROR statement
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