Στις Friday 21 January 2011 22:22:24 ο/η Tom Lane έγραψε:
> "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
> > Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >> If it should be less than 1, then what?
>
> > 1 - (estimated tuples / estimated distinct values) ?
>
> Uh, no. The number we're after is the probability that an outer tuple
> has at least one unequal value in the inner relation. This is not 1
> minus the probability that a *specific* inner value is equal, which is
> what I think your formula is estimating.
Isn't this probablity (an outer tuple has at least one unequal value in the inner relation)
= 1 - (probability that all values in the inner relation are equal to the value of the outer tuple)
Anyways, glad to see smth came out of this.
Thx
>
> regards, tom lane
>
--
Achilleas Mantzios