Re: more on delete from join
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sat, 29 Aug 2009 17:40:04 -0300
Message-ID: <4a99922d$0$23747$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.
Date: Sat, 29 Aug 2009 17:40:04 -0300
Message-ID: <4a99922d$0$23747$9a566e8b_at_news.aliant.net>
Kevin Kirkpatrick wrote:
> On Aug 29, 9:45 am, Bob Badour <bbad..._at_pei.sympatico.ca> wrote: >
>>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.
> > > What should these clear and elegant programs print? > > int x, y; > y:=3; > x:=y; > print (x); > y:=4; > print (x); > -------- > int x, y; > y:=3; > x+y:=5; > print(x); > y:=4; > print(x);
Sorry, I guess I misspoke.
x+y=3
x-y=1
is clear and elegant. The crap the semi-colons and square brackets is crap. Received on Sat Aug 29 2009 - 22:40:04 CEST