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Don't install ICU collation keyword variants

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Users can still create them themselves.  Instead, document Unicode TR 35
collation options for ICU, so users can create all this themselves.

Reviewed-by: Peter Geoghegan <pg@bowt.ie>
This commit is contained in:
Peter Eisentraut
2017-08-21 11:22:00 -04:00
parent 51e225da30
commit 2bfd1b1ee5
2 changed files with 84 additions and 85 deletions
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98
doc/src/sgml/charset.sgml
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@ -664,13 +664,6 @@ SELECT a COLLATE "C" &lt; b COLLATE "POSIX" FROM test1;
</listitem>
</varlistentry>
<varlistentry>
<term><literal>de-u-co-phonebk-x-icu</literal></term>
<listitem>
<para>German collation, phone book variant</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>de-AT-x-icu</literal></term>
<listitem>
@ -683,13 +676,6 @@ SELECT a COLLATE "C" &lt; b COLLATE "POSIX" FROM test1;
</listitem>
</varlistentry>
<varlistentry>
<term><literal>de-AT-u-co-phonebk-x-icu</literal></term>
<listitem>
<para>German collation for Austria, phone book variant</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>und-x-icu</literal> (for <quote>undefined</quote>)</term>
<listitem>
@ -709,6 +695,90 @@ SELECT a COLLATE "C" &lt; b COLLATE "POSIX" FROM test1;
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
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 "de-u-co-phonebk-x-icu" (provider = icu, locale = 'de-u-co-phonebk')</literal></term>
<listitem>
<para>German collation with phone book collation type</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>CREATE COLLATION "und-u-co-emoji-x-icu" (provider = icu, locale = 'und-u-co-emoji')</literal></term>
<listitem>
<para>
Root collation with Emoji collation type, per Unicode Technical Standard #51
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>CREATE COLLATION digitslast (provider = icu, locale = 'en-u-kr-latn-digit')</literal></term>
<listitem>
<para>
Sort digits after Latin 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>
<varlistentry>
<term><literal>CREATE COLLATION numeric (provider = icu, locale = 'en-u-kn-true')</literal></term>
<listitem>
<para>
Numeric ordering, sorts sequences of digits by their numeric value,
for example: <literal>A-21</literal> &lt; <literal>A-123</literal>
(also known as natural sort).
</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. The list of possible collation types (<literal>co</literal>
subtag) can be found in
the <ulink url="http://www.unicode.org/repos/cldr/trunk/common/bcp47/collation.xml">CLDR
repository</ulink>.
The <ulink url="https://ssl.icu-project.org/icu-bin/locexp">ICU Locale
Explorer</ulink> can be used to check the details of a particular locale
definition.
</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>