Re: more on delete from join

From: Bob Badour <>
Date: Sat, 29 Aug 2009 11:44:19 -0300
Message-ID: <4a993ecb$0$23766$>

paul c wrote:

> Bob Badour wrote:

>> Kevin Kirkpatrick wrote:
>>> On Aug 28, 4:32 pm, paul c <> wrote:
>>>> Kevin Kirkpatrick wrote:
>>>> ...
>>>>>> By the way, why assume that CURRENT_USER
>>>>>> is not updateable?
>>>>> Great question, cuts to the heart of the matter: It can't be updated
>>>>> because it is a view. It returns an conclusion, and it is not (IMO)
>>>>> valid to assert conclusions. ...
>>>> So A UNION B is a conclusion when assigned to a view, but not a
>>>> conclusion when assigned to a base. Where does this idea come from and
>>>> what is it good for, apart from appearing to be a spurious reason to
>>>> say
>>>> that views aren't updateable? Even if I were to accept that views
>>>> aren't updateable, I'd ask why is CURRENT_USER necessarily a view?
>>>> (Personally, I would prefer an engine that allows a user to log himself
>>>> off by means of a simple delete rather than the usual arcane engine
>>>> plumbing that introduces various environmental commands. That way, the
>>>> environment is forced to react to db changes rather than the other way
>>>> around. The engine becomes much simpler if this approach is followed
>>>> and this is important if there's ever to be any progess in the aspects
>>>> that today's engines slough off.)
>>>> ...
>>> My point, phrased another way, is: given base relvars A, B, and C with
>>> identical headings, this does not make sense:
>>> (A UNION B) := (B UNION C)
>>> in the exact same way that this does not make sense:
>>> int x, y;
>>> x+y := 3;
>> But computers do solve systems of equations:
>> x+y = 3
>> x-y = 1
> That seems a very useful interpretation to me, maybe much better than my 
> argument, interpretation is a big and tricky area, coalescing an 
> accurate interpretation with a useful one is a talent Codd had.

I cannot take credit for it. From what I understand, the whole point of the work Vadim and Marshall have done is to find a way to solve systems of relational equations and what Marshall once told me leads me to suspect the idea originates with Vadim. Received on Sat Aug 29 2009 - 16:44:19 CEST

Original text of this message