Re: is pivoted phones view updateable?

From: NENASHI, Tegiri <tnmail42_at_gmail.com>
Date: Wed, 15 Nov 2006 04:51:57 +0100 (CET)
Message-ID: <Xns987BE90C850C3asdgba@194.177.96.26>

"Vadim Tropashko" <vadimtro_invalid_at_yahoo.com> wrote in news:1163552934.435256.253050_at_e3g2000cwe.googlegroups.com:

>
> NENASHI, Tegiri wrote:

>> "Vadim Tropashko" <vadimtro_invalid_at_yahoo.com> wrote in
>> news:1163523276.819401.288540_at_m7g2000cwm.googlegroups.com:
>>
>> > NENASHI, Tegiri wrote:
>> >> The view is not correct:  suppose (2) has not the FAX.  One goes
>> >> to lose (2) in the view oldcontactview.
>> >
>> > The view (2) is supposed to reflect the data in the table
>> >
>> > ID      VOICE   FAX
>> > 1       4150000000      4081111111
>> > 2       80012345672     6501234567
>> >
>> > which doesn't have NULLs. Perhaps this should be stated as an
>> > explicit constraint?
>>
>> Pardon me but you did not understand well what I have wrote:

>
> indeed
>

>> Suppose that the row with id = 2 of the newcontact table has not the
>> fax number.  You go to lose the personne whose id = 2 in the view
>> oldcontactview.  What you do in this situation ?

>
> This has been vaguely mentioned in the other thread. There are
> implicit constraints in a view that must not allow such updates.

Very well, is it that direct inserts into the newcontact table are not permitted and one can utilize only the view ?

>
> Consider the function
>
> y = 2*x
>
> on the domain of integers. Scalar value "x" is analogous to a a
> relational variable, and scalar value "y" corresponds to a view. I can
> change the state of x to any integer value. I cannot change the value
> of y to anything, because there is an implicit constraint that the
> range of y is that of even numbers.

It is obvious.

>> > Regardless, the example in the beginning of the thread is even more
>> > simple (and NULL immune). Although, it seems to require a whole lot
>> > of algebraic manipulations to invert it.
>>
>> I do not understand all the notation.

>
> This is why it is kept to the minimum?-) OK, clearly you know what /\
> and \/ is. Next, 00 is an empty relation with empty attribute set.
> Finally, 01 is the relation with empty attribute set and one tuple (it
> is the bottom element in the lattice). Did I miss anything else?
>

I shall think about it.

--
Tegi

Received on Tue Nov 14 2006 - 21:51:57 CST