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

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От Simon Riggs
Тема Re: Allowing extensions to supply operator-/function-specific info
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Msg-id CANP8+jLMj6xwZ_1kBXD_CAfMKPo1Hvo=HvEgqbg+va6k5DGoCQ@mail.gmail.com
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Ответ на Re: Allowing extensions to supply operator-/function-specific info  (Tom Lane <tgl@sss.pgh.pa.us>)
Ответы Re: Allowing extensions to supply operator-/function-specific info  (Tom Lane <tgl@sss.pgh.pa.us>)
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On Sun, 27 Jan 2019 at 19:17, Tom Lane <tgl@sss.pgh.pa.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 

--
Simon Riggs                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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