Re: Surjective functional indexes

Re: Konstantin Knizhnik 2017-05-30 <f97118e3-821c-10a8-85ec-0af3f1dfd01d@postgrespro.ru>
> 
> 
> On 29.05.2017 20:21, Christoph Berg wrote:
> > 
> > I think the term you were looking for is "projection".
> > 
> > https://en.wikipedia.org/wiki/Projection_(set_theory)
> 
> I have already renamed parameter from "surjective" to "injective".
> But I am ok to do do one more renaming to "projection" if it will be
> considered as better alternative.
> From my point of view, "projection" seems to be clearer for people without
> mathematical background,
> but IMHO this term is overloaded in DBMS context.

With mathematical background, I don't see how your indexes would
exploit surjective or injective properties of the function used. What
you are using is that ->> projects a json value to one of its
components, i.e. the projection/function result does not depend on the
other attributes contained.

> The irony is that in Wikipedia "projection" is explained using
> "surjection" term:)

For the equivalence classes part, which isn't really connected to your
application.

Christoph