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# Re: What databases have taught me

Date: Sat, 24 Jun 2006 01:36:07 GMT
Message-ID: <bG0ng.1350\$pu3.36337@ursa-nb00s0.nbnet.nb.ca>

Aloha Kakuikanu wrote:

>

>>Aloha Kakuikanu wrote:
>>
>>
>>>Keith H Duggar wrote:
>>>
>>>
>>>>http://dbappbuilder.sourceforge.net/Rel.html
>>>
>>>
>>>Speaking of clumsy syntax, why
>>>
>>>R WHERE x = 1 AND y = 2
>>>
>>>and not
>>>
>>>R AND x = 1 AND y = 2
>>>
>>>?
>>
>>Would (R AND x = 1 AND y = 2) = (x = 1 AND y = 2 AND R) ?

>
>
> Yes
>
>
>>If so, wouldn't that make name resolution kinda complicated and perhaps
>>error-prone?

>
>
> I'm not clear what do you mean by name resolution. The expression
> appeals from sql optimization perspective: it's a join of 3 finite
> relations. There are 6 join order permutations possible:
>
> i). x = 1 join y = 2 join R
> ii). x = 1 join R join y = 2
> iii). x = 2 join R join y = 1
> iv). x = 2 join y = 1 join R
> v). R join y = 2 join x = 1
> vi). R join y = 1 join x = 2
>
> Evaluate cost of each and execute the one with lowest cost!

Consider:

Ra = Rb AND x = 1 AND y = 1

Where Ra and Rb are two relvars. Is that still a join? To what do x and y refer?

Consider:

R AND x = 1 AND y = 1

where R has no x attribute. Will that cause a compile-time error? Why or why not? Received on Fri Jun 23 2006 - 20:36:07 CDT

Original text of this message

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