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From "George Baklarz (JIRA)" <derby-...@db.apache.org>
Subject [jira] Created: (DERBY-172) Trigger activation
Date Fri, 11 Mar 2005 00:10:55 GMT
Trigger activation
------------------

         Key: DERBY-172
         URL: http://issues.apache.org/jira/browse/DERBY-172
     Project: Derby
        Type: Bug
  Components: Documentation  
    Versions: 10.0.2.0    
 Environment: Windows XP SP1 Windows
    Reporter: George Baklarz
    Priority: Minor


I image that this is a documentation problem. The "words" around triggers seem to imply the
ability to do actions "BEFORE" the INSERT/UPDATE/DELETE. For instance:

"Along with constraints, triggers can help enforce data integrity rules with actions such
as cascading deletes or updates. Triggers can also perform a variety of functions such as
issuing alerts, updating other tables, sending e-mail, and other useful actions."

Well, the CREATE TRIGGER command only allows AFTER as an option (even though the SYSTRIGGERS
catalog uses "B" for before and "A" for after) and it won't allow a CALL statement to be processed.
Seems to me that there aren't any ways to send an e-mail, issue alerts (no SIGNAL function
either), or enforce integrity rules. How can you enforce integrity rules if invalid data comes
in? I can't force a SIGNAL or error with the trigger, so this is useless for validating changes
to the data.

In addition, there appears to be some logic regarding BEFORE triggers in Derby, but its not
currently working.

CREATE TRIGGER CB NO CASCADE BEFORE
   INSERT ON BONUSES
      REFERENCING NEW AS n
      FOR EACH ROW MODE DB2SQL
      UPDATE BONUSES
         SET BONUS =
             CASE
                WHEN (n.BONUS = 0) THEN 100
                ELSE n.BONUS
             END;
ERROR 42Z9D: 'UPDATE' statements are not allowed in 'BEFORE' triggers.

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