From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
Cc: | pageorge(at)unice(dot)fr, Pg Docs <pgsql-docs(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Does the POSITION() function takes into account the COLLATION... or not ?!? |
Date: | 2022-02-16 16:18:46 |
Message-ID: | 3324021.1645028326@sss.pgh.pa.us |
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"David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> On Tue, Feb 15, 2022 at 11:17 AM PG Doc comments form <
> noreply(at)postgresql(dot)org> wrote:
>> ==> up to here, this seems pretty enough to conclude that POSITION()
>> doesn't
>> care at all about COLLATION and always perform a byte search.
> How collations behave is documented, in particular:
> "A collation is either deterministic or nondeterministic. A deterministic
> collation uses deterministic comparisons, which means that it considers
> strings to be equal only if they consist of the same byte sequence."
Right. POSITION does indeed do bytewise search, which is a legal
implementation for any deterministic collation, but perhaps not
for a nondeterministic one. Thus, it throws a feature-not-supported
error if asked to use a nondeterministic collation. As you say,
this is far from the only function that acts that way.
regards, tom lane
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