| From: | Christoph Berg <myon(at)debian(dot)org> |
|---|---|
| To: | Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Surjective functional indexes |
| Date: | 2017-09-13 10:14:59 |
| Message-ID: | 20170913101459.bj6f4wiplvyxup5n@msg.df7cb.de |
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Re: Konstantin Knizhnik 2017-09-13 <2393c4b3-2ec4-dc68-4ea9-670597b561fe(at)postgrespro(dot)ru>
>
>
> On 13.09.2017 10:51, Christoph Berg wrote:
> > Re: Konstantin Knizhnik 2017-09-01 <f530ede0-1bf6-879c-c362-34325514f692(at)postgrespro(dot)ru>
> > > + Functional index is based on on projection function: function which extract subset of its argument.
> > > + In mathematic such functions are called non-injective. For injective function if any attribute used in the indexed
> > > + expression is changed, then value of index expression is also changed.
> > This is Just Wrong. I still think what you are doing here doesn't have
> > anything to do with the function being injective or not.
>
> Sorry, can you please explain what is wrong?
I don't get why you are reasoning about "projection" ->
"non-injective" -> "injective". Can't you try to explain what this
functionality is about without abusing math terms that just mean
something else in the rest of the world?
Christoph
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