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From: Tom Lane <[email protected]>
To: David G. Johnston <[email protected]>
Cc: [email protected]
Cc: Pg Docs <[email protected]>
Subject: Re: Does the POSITION() function takes into account the COLLATION... or not ?!?
Date: Wed, 16 Feb 2022 11:18:46 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAKFQuwavkvERHKc=-Ws=1YEXy68j4GpJx0XbUwbKbY-=hKs7zQ@mail.gmail.com>
References: <[email protected]>
	<CAKFQuwavkvERHKc=-Ws=1YEXy68j4GpJx0XbUwbKbY-=hKs7zQ@mail.gmail.com>

"David G. Johnston" <[email protected]> writes:
> On Tue, Feb 15, 2022 at 11:17 AM PG Doc comments form <
> [email protected]> 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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