Re: GSoC 2017: Foreign Key Arrays

On Mon, Jul 31, 2017 at 5:18 PM, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
wrote:

> Tom Lane wrote:
> > Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> > > ... However, when you create an index, you can
> > > indicate which operator class to use, and it may not be the default
> one.
> > > If a different one is chosen at index creation time, then a query using
> > > COUNT(distinct) will do the wrong thing, because DISTINCT will select
> > > an equality type using the type's default operator class, not the
> > > equality that belongs to the operator class used to create the index.
> >
> > > That's wrong: DISTINCT should use the equality operator that
> corresponds
> > > to the index' operator class instead, not the default one.
> >
> > Uh, what? Surely the semantics of count(distinct x) *must not* vary
> > depending on what indexes happen to be available.
>
> Err ...
>
> > I think what you meant to say is that the planner may only choose an
> > optimization of this sort when the index's opclass matches the one
> > DISTINCT will use, ie the default for the data type.

I understand the problem. I am currently researching how to resolve it.

Best Regards,
Mark Rofail