Ashutosh Bapat wrote:
> On Mon, Jun 5, 2017 at 8:22 AM, atorikoshi
> <torikoshi_atsushi_z2@lab.ntt.co.jp> wrote:
> > Hi,
> >
> > I found below formula to compute selectivities, but
> > I think the last Probability 'P(b=?)' should be 'P(c=?)'.
> >
> >> P(a=?,b=?,c=?) = P(a=?,b=?) * (d + (1-d)*P(b=?))
> >
> >
> > Attached patch fixes it, and it also adds some spaces
> > following another formula which is on line 86 and
> > computes P(a=?, b=?).
>
> Agree. Also using "d" for "degree of functional dependence (b=>c) as
> well is confusing. We are already using "d" for "degree of functional
> dependence (a=>b). Here' patch to use "d'" instead of "d".
Since the surrounding text uses single quotes to talk about each letter,
I thought it was better to use a new letter (e) so that we don't require
the "prime" notation, which would end up being either inconsistent,
confusing, stupid-looking, or combinations thereof.
Also, your proposed text had a slight mistake: it's not (b=>c) that
d' is for, but (a,b=>c).
Pushed with those corrections.
Thanks for the reports and patches!
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
