Re: more on delete from join

From: Tegiri Nenashi <tegirinenashi_at_gmail.com>
Date: Tue, 1 Sep 2009 08:29:51 -0700 (PDT)
Message-ID: <6210e650-37bb-400b-931c-0e4c73357c00_at_y4g2000prf.googlegroups.com>



On Sep 1, 8:03 am, Kevin Kirkpatrick <kvnkrkpt..._at_gmail.com> wrote:
> Looking at an even simpler example, we encounter the same problem:
> VIEW F := 'E';
> DELETE FROM F {{C2='B'}}
>
> This yields the system of equations
> E = E MINUS {{C2='B'}}
> which is solved by any of these assignments:
> E := {{}}
> E := {{C2='A'}}
> E := {{C2='A'}, {C2='Q'}}
> ...

You are correct: the approach should handle at least trivial view updates. The system of equation is:

F = E
F minus deltaF = E minus {{C2='B'}}
"deltaF and F have the same set of attributes" -- (that is a constraint as well!)

The system is still underspecified for E and F -- the question is if it is underspecified for deltaF! Received on Tue Sep 01 2009 - 10:29:51 CDT

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