Re: projection with nulls

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sun, 16 Mar 2008 20:55:06 -0300
Message-ID: <47ddb35b$0$4041$9a566e8b_at_news.aliant.net>

paul c wrote:

> David Cressey wrote:
> 

>> ...
>> I have always treated GROUP BY and SELECT DISTINCT as providing the
>> functionality that's closest to projection.
>>
>> Some dialects of SQL will indeed eliminate the second tuple if GROUP
>> BY or
>> SELECT DISTINCT are used.
>> ...
>
> What is SQL's SELECT but projection?

The select list is a combination of project and extend. The from clause is cartesian product and/or join and/or union (outer join). THe where clause is restrict.
The group by clause is a curious sort of project that's required for aggregation.
The having clause is restrict again. Received on Mon Mar 17 2008 - 00:55:06 CET