Re: Allowing extensions to supply operator-/function-specific info

On Sun, 27 Jan 2019 at 19:17, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> > * Allow a normal term to match a functional index, e.g. WHERE x =
> > 'abcdefgh' => WHERE substr(x, 1 , 5) = 'abcde' AND x = 'abcdefgh'
>
> I'm a bit confused about what you think this example means. I do
> intend to work on letting extensions define rules for extracting
> index clauses from function calls, because that's the requirement
> that PostGIS is after in the thread that started this. I don't
> know whether that would satisfy your concern, because I'm not clear
> on what your concern is.
>

To be able to extract indexable clauses where none existed before.

Hash functions assume that x = N => hash(x) = hash(N) AND x = N
so I want to be able to assume
x = K => f(x) = f(K) AND x = K
for specific f()
to allow indexable operations when we have an index on f(x) only

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Simon Riggs http://www.2ndQuadrant.com/
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