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Date: Thu, 7 May 2009 14:26:45 -0700 (PDT)
From: "Kathey Marsden (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Updated: (DERBY-172) Improve documentation for BEFORE
 triggers
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     [ https://issues.apache.org/jira/browse/DERBY-172?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Kathey Marsden updated DERBY-172:
---------------------------------

    Summary: Improve documentation for BEFORE triggers  (was: Trigger activation)

Changing title to better reflect the user request for better documentation for BEFORE triggers.


> Improve documentation for BEFORE triggers
> -----------------------------------------
>
>                 Key: DERBY-172
>                 URL: https://issues.apache.org/jira/browse/DERBY-172
>             Project: Derby
>          Issue Type: Bug
>          Components: Documentation
>    Affects 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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