| From: | Christoph Berg <myon(at)debian(dot)org> |
|---|---|
| To: | Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru> |
| Cc: | Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Surjective functional indexes |
| Date: | 2017-05-30 17:01:17 |
| Message-ID: | 20170530170117.gnsd7kne6jovvpur@msg.df7cb.de |
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| Lists: | pgsql-hackers |
Re: Konstantin Knizhnik 2017-05-30 <f97118e3-821c-10a8-85ec-0af3f1dfd01d(at)postgrespro(dot)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
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