Re: insert to projection

From: paul c <toledobythesea_at_oohay.ac>
Date: Sat, 05 Sep 2009 02:38:10 GMT
Message-ID: <makom.43821$PH1.9329_at_edtnps82>



Tegiri Nenashi wrote:
> ...
> I suggest that the idea that we focus on basic relational algebra
> operators, figure out which updates of these are legitimate, then
> leverage this knowledge for complex view updates is fundamentally
> wrong. Consider a "pivot" view:
>
> table Contacts (
> name String,
> email String,
> phone String
> )
>
> and the view
>
> select name, email as contact, 'email' as type
> union
> select name, phone as contact, 'phone' as type
>
> This is a perfectly updatable view, yet your approach would fail to
> discover how to translate its update to the base table. (This pivot
> operation is a recurrent theme in data exchanges)
> ...
  1. I don't know what 'as' means here. If the result of the union is a relation, then "as" terms are completely meaningless, the union would be a disjunction with attributes name, email, phone or attributes name, contact, type. How does that change any question, whether it is update, insert or delete?
  2. I haven't talked about updating a union, but if I had I would have distinguised between insert and delete. In this thread I've only had projections in mind.
Received on Fri Sep 04 2009 - 21:38:10 CDT

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