On 8/9/17 18:49, Peter Geoghegan wrote:
> I'd like to give a demo on what is already possible, but not currently
> documented. I didn't see anyone else comment on this, including Peter
> E (maybe I missed that?). We should improve the documentation in this
> area, to get this into the hands of users.
Here is a small piece of documentation. Thoughts?
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Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
From a9d5926b68eb6e0e726b7c9838f6ea8b3b22a157 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <pete...@gmx.net>
Date: Tue, 15 Aug 2017 14:31:39 -0400
Subject: [PATCH] doc: Document TR 35 collation options for ICU
---
doc/src/sgml/charset.sgml | 52 +++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 52 insertions(+)
diff --git a/doc/src/sgml/charset.sgml b/doc/src/sgml/charset.sgml
index 48ecfc5f48..7bb645a39f 100644
--- a/doc/src/sgml/charset.sgml
+++ b/doc/src/sgml/charset.sgml
@@ -709,6 +709,58 @@ <title>ICU collations</title>
will draw an error along the lines of <quote>collation "de-x-icu" for
encoding "WIN874" does not exist</>.
</para>
+
+ <para>
+ ICU allows collations to be customized beyond the basic
+ language/country/type set that is preloaded by <command>initdb</command>.
+ Users are encouraged to define their own collation objects that make use
+ of these facilities to suit the sorting behavior to their requirements.
+ Here are some examples:
+ <variablelist>
+ <varlistentry>
+ <term><literal>CREATE COLLATION digitslast (provider = icu, locale =
'en-u-kr-latn-digit')</literal></term>
+ <listitem>
+ <para>
+ Sort digits after letters. (The default is digits before letters.)
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>CREATE COLLATION upperfirst (provider = icu, locale =
'en-u-kf-upper')</literal></term>
+ <listitem>
+ <para>
+ Sort upper-case letters before lower-case letters. (The default is
+ lower-case letters first.)
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>CREATE COLLATION special (provider = icu, locale =
'en-u-kf-upper-kr-latn-digit')</literal></term>
+ <listitem>
+ <para>
+ Combines both of the above options.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+
+ See <ulink
url="http://unicode.org/reports/tr35/tr35-collation.html";>Unicode
+ Technical Standard #35</ulink>
+ and <ulink url="https://tools.ietf.org/html/bcp47";>BCP 47</ulink> for
+ details.
+ </para>
+
+ <para>
+ Note that while this system allows creating collations that <quote>ignore
+ case</quote> or <quote>ignore accents</quote> or similar (using
+ the <literal>ks</literal> key), PostgreSQL does not at the moment allow
+ such collations to act in a truly case- or accent-insensitive manner. Any
+ strings that compare equal according to the collation but are not
+ byte-wise equal will be sorted according to their byte values.
+ </para>
</sect4>
</sect3>
--
2.14.1
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