Re: Relation subset operators

On 6 juin, 14:32, paul c <toledobythe..._at_oohay.ac> wrote:
> Walter Mitty wrote:
>
> ...
>
> > Here's an attempt in Spanish
>
> > "Si el conjunto de autos morados fuese un conjunto vacío,
> > entonces ningun vendedor no podría vender auto morado alguno
> > (nisiquiera uno) de tal modo que todos los vendedores
> > los han vendido todos. "
>
> > It sounds equally absurd to me.  I'm not sure it's right.
> > Note the double negative, and the use of a subjunctive.
> > ...
>
> Thanks.  Good observations, one could say such queries are indeed
> subjunctive (maybe all queries are), here's Date's SQL for "Get
> suppliers who supply all purple parts":
>
> SELECT DISTINCT s.*
> FROM S AS s
> WHERE NOT EXISTS
>               ( SELECT DISTINCT p.*
>                 FROM   P AS p
>                 WHERE p.COLOR = 'Purple'
>                 AND      NOT EXISTS
>                            ( SELECT DISTINCT sp.*
>                              FROM   SP AS p
>                              WHERE s.S# = sp.S#
>                              AND       sp.P# = p.P# ) ).
>
> If I'm not mistaken the answer is that all suppliers supply no purple
> parts.  Just a consequence of FOPC.
>
> > A guy walks into a coffee shop, and orders a coffee without cream.
> > The server says, "we're all out of cream today."
> > "In that case," the guy responds, "I'll have a cup of coffee without milk."
>
> You might've hit the nail on the head (which the SQL accomplishes rather
> extravagantly by using a wrench instead of a hammer).  They did that
> joke in a Marlene Dietrich movie, cafe scene where the guy hustling her
> and the (French) waiter can't take their eyes off her.  Hustler asks for
> coffee with no cream.  Waiter says there is no cream, would coffee with
> no milk do?  So the coffee was the same, no matter whether it had no
> cream or no milk.  Perhaps a viewpoint that life is subjunctive is the
> first baby step for escape from mysticism..

In a way that gave to think that relational model is *not* ready yet to apply absurd mathematical reasonning yet. Be it finally sound or not, absurd logical reasonning is too risky for a young science to be used as a foundation . I will stick to basic clarifications on a step y step basis and let the big theories to smarter people.

Regards... Received on Sat Jun 06 2009 - 17:14:08 CEST