Re: more on delete from join
Date: Sat, 29 Aug 2009 11:45:32 -0300
Message-ID: <4a993f13$0$23766$9a566e8b_at_news.aliant.net>
Kevin Kirkpatrick wrote:
> On Aug 28, 6:29 pm, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>
>>Kevin Kirkpatrick wrote:
>>
>>>On Aug 28, 4:32 pm, paul c <toledobythe..._at_oohay.ac> 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
> > Well, I will grant that. But there is an difference between > > exp[0]:='x+y = 3' > exp[1]:='x-y = 1' > print(Solve_system (exp, 'x')); -- prints 2 > > and > x+y := 3; > x-y := 1; > print (x); -- prints 2? (does it? can it? see below...)
I agree. The former is klunky and inelegant while the latter is elegant and clear. Received on Sat Aug 29 2009 - 16:45:32 CEST