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From "Kaydell On His PC" ...@kaydell.com>
Subject unsubscribe
Date Tue, 21 Jul 2009 07:44:06 GMT

----- Original Message ----- 
From: "Rick Hillegas" <Richard.Hillegas@Sun.COM>
To: "Derby Discussion" <derby-user@db.apache.org>
Sent: Monday, July 06, 2009 10:11 AM
Subject: Re: automatically (re)computing last modified time?


> Hi Peri,
> 
> Yes, I think that triggers would be your best solution for this problem.
> 
> You could use a generation clause to stuff the timestamp field via a 
> function which returns the current time given all of the other columns 
> as arguments. This would be an awkward solution for the following reasons:
> 
> 1) Dishonesty. When you registered this function with Derby, you would 
> have to lie and say that it is deterministic.
> 
> 2) Brittleness. If you added another column to the table, then the 
> function would not be fired when you updated the new column. That is 
> because the generation clause didn't mention the new column. To get 
> around this problem, every time you added a new column to the table, you 
> would have to change the signature of your function and drop and 
> recreate the generated column.
> 
> Hope this helps,
> -Rick
> 
> Peri Tarr wrote:
>> Hello,
>>
>> For each update to a row in a particular table, I would like to store 
>> the last user who modified it and the timestamp when it was modified. 
>> I had thought to use Derby's nifty GENERATED ALWAYS for these:
>>
>>      alter table people add lastModified GENERATED ALWAYS AS 
>> (CURRENT_TIMESTAMP);
>>      alter table people add lastModifiedBy GENERATED ALWAYS AS 
>> (CURRENT_USER);
>>
>> Unfortunately, neither CURRENT_TIMESTAMP nor CURRENT_USER are 
>> permitted for automatically generated columns (the documentation says 
>> so; I just hadn't noticed).
>>
>> Is the intent for people to do this with triggers or some other mechanism?
>>
>> Thanks very much in advance!
>>      Peri
>

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