| From: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Super PathKeys (Allowing sort order through precision loss functions) |
| Date: | 2018-10-31 23:19:32 |
| Message-ID: | CAKJS1f-mCJ5RdkhyCPa8Vrrts6cS3mD1gteOtoZ5fgM+C5UB9Q@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 1 November 2018 at 12:11, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
> I still have trouble imagining what exactly would the function do to
> determine if the optimization can be applied to substr() and similar
> collation-dependent cases.
I guess the function would have to check for a Const offset of 0, and
a collection, perhaps of "C" for the 1st arg. In any case, I wouldn't
want this idea to be hung up on the fact we can't determine how to
make substr() work correctly with it.
I'm most interested in date_trunc() and friends. A first cut
implementation would not have to implement functions for everything
that's possible to implement.
--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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