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Re: Tutorial D with + restrict

From: Strider <Anymore_at_short.int>
Date: Thu, 30 Mar 2006 14:11:14 +0200
Message-ID: <Xns979690520D71strider5athome@195.34.135.101>


>

>> WITH ( SP RENAME ( SNO AS X ) ) AS R :
>> EXTEND ( S { SNO } ) ADD ( COUNT ( R WHERE X = SNO ) AS NP )

>
> It appears to be a join of
> select sno, count(*) as np from sp group by sno
> with
> select sno from s
> on sno
>

Yes that is exactly what i have thought.

> What RESTRICT ? I see WHERE in the scope of EXTEND in there.

Yes EXTEND is a keyword here, you have given me right direction, thank you.

EXTEND A ADD exp AS Z is a relation with: ...
A body consisting of all tuples t such that t is a tuple of A extended with a value for attribute Z that is computed by *evaluating* exp on *that* tuple of A.

Thank you. Received on Thu Mar 30 2006 - 06:11:14 CST

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