Re: question about query optimizer


"Jan M. Nelken" <Unknown.User@xxxxxxxxxxxxxx> wrote in message
news:b--dnZIDmfoaRNDeRVn-sQ@xxxxxxxxxxxxx
> Charles Lee wrote:
> > "Jim Kennedy" <kennedy-downwithspammersfamily@xxxxxxxxx> дÈëÏûÏ¢ÐÂÎÅ
> > :4vydnaeBW4dNKNDeRVn-gw@xxxxxxxxxxxxxx
> >
> >
> >>go to unknowndatabase.com and click on the white paper link.
> >>Hard to comment on that.
> >
> >
> >
> > Thanks Jim, but that link is broken somehow ...
> >
> >
>
> Pleeeasee - since you clearly specified database engine - Jim replied with
> matching URL ...
>
> Jan M. Nelken

<joke begin>
We know it isn't true of the Mauve database because it uses more RAM.
</joke end>

Since some people didn't get the joke let me say this. Different databases
have different optimizers. For someone to make a blanket statement would be
silly. Sure it is possible that some vendor's optimizer in some particular
cases might take longer to optimize than to run the other steps of the
query. (remember people can write crappy sql also, but even subtracting
those cases out, it could happen) I could have been a wisenhimer and say
yeah I head that was true of (insert name of some database her) database.
It would be a silly statement and would just start a flame war.

Think about the problem. If someone issues a query with 35 tables in the
query then the optimizer has to figure out what order to go after the data.
Where should it start? It has a huge number of permutations (35!) to
consider. If it doesn't have any statisstics about the data it might not
make a good choice.

I'm sure if you did a google search you could find vendor X saying vendor Y
has an optimizer that...
Jim


.

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