From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com>, Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at>, 'pinker *EXTERN*' <pinker(at)onet(dot)eu>, "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: Shouldn't "WHEN (OLD.* IS DISTINCT FROM NEW.*)" clause be independent from data type? |
Date: | 2015-09-17 17:50:18 |
Message-ID: | 20150917175018.GZ88970@alvherre.pgsql |
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Lists: | pgsql-general |
Tom Lane wrote:
> Since type record *does* have btree/hash opclasses, it is not negotiable
> that the component column types obey btree or at least hash semantics.
> The only way to fix this would be to provide such opclasses for point.
> Btree has the probably-fatal obstacle that there's no plausible linear
> sort order for 2-D points. It would be possible to make hash work, if
> it weren't that point_eq() is fuzzy equality not exact equality.
This comment made me remember something I mentioned some months ago,
regarding fuzzy comparisons for other datatypes;
http://www.postgresql.org/message-id/20150512181307.GJ2523@alvh.no-ip.org
It seems that currently box_contains_pt() uses exact floating point
operators rather than fuzzy; we were pushing for having some of these
operators be changed to use the fuzzy definitions, and introduce a few
more fuzzy operators, to be used in BRIN opclasses.
I wonder if it would make sense to introduce a hash opclass for point
and other floating-point-based datatypes that uses strict equality, so
that IS [NOT] DISTINCT FROM works on them. Since there cannot be a
btree opclass for point, there shouldn't be any definitional problem in
doing so; but for datatypes that do have a linear sort order, maybe this
(having different equality operators for btree and hash) would be a
problem.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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