Re: Foreign key problem
From: paul c <toledobythesea_at_oohay.ac>
Date: Thu, 15 Jun 2006 18:41:04 GMT
Message-ID: <4Rhkg.32844$iF6.7247_at_pd7tw2no>
>
> As in the example. I interpreted the 'foreign_keys(...)'
> stanzas to be some sort of expressions of some sort of super
> constraint in which two of three referring columns had the
> same referents. What are those expressions? I don't know.
> What are super constraints? I don't know.
>
> Did you have any specific reason for re-specifying those?
>
>
> Funky. But fine by me.
>
> not(cardinality(t1) > cardinality(t2{c} intersect t2{d})), right?
Date: Thu, 15 Jun 2006 18:41:04 GMT
Message-ID: <4Rhkg.32844$iF6.7247_at_pd7tw2no>
Jay Dee wrote:
> x wrote:
>> "Jay Dee" <ais01479_at_aeneas.net> wrote in message >> news:svbkg.68231$P2.43250_at_tornado.ohiordc.rr.com... >> >>> Hmm. A _name_ /would/ be necessary to permit your example.. >> >> I know. But it shouldn't be. >> >>> But what is the meaning of the overlapping constraints >>> with different names? >> >> Overlapping as in the example, or overlapping as identical ?
>
> As in the example. I interpreted the 'foreign_keys(...)'
> stanzas to be some sort of expressions of some sort of super
> constraint in which two of three referring columns had the
> same referents. What are those expressions? I don't know.
> What are super constraints? I don't know.
>
> Did you have any specific reason for re-specifying those?
>
>> How about this: >> >> t1(a,b) >> t2(c,d) >> >> (a,b) references (c,d) >> (b,a) references (c,d)
>
> Funky. But fine by me.
>
> not(cardinality(t1) > cardinality(t2{c} intersect t2{d})), right?
It all seems like fiddlesticks to me. If two input tables or relations aren't comparable I doubt if there is any logical way to compare them, so to envisage that there is such a way if it is given that they may or may not be comparable seems like a mug's game.
I believe the inputs the OP gave originally were comparable, therefore joinable.
p Received on Thu Jun 15 2006 - 20:41:04 CEST