Re: Surjective functional indexes

Re: Konstantin Knizhnik 2017-09-13 <2393c4b3-2ec4-dc68-4ea9-670597b561fe@postgrespro.ru>
> 
> 
> On 13.09.2017 10:51, Christoph Berg wrote:
> > Re: Konstantin Knizhnik 2017-09-01 <f530ede0-1bf6-879c-c362-34325514f692@postgrespro.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