linkend="icu-language-tag">Language Tag</link>.

<programlisting>

CREATE COLLATION mycollation1 (PROVIDER = icu,LOCALE = 'ja-JP');

CREATE COLLATION mycollation2 (PROVIDER = icu,LOCALE = 'fr');

CREATE COLLATION mycollation1 (provider = icu,locale = 'ja-JP');

CREATE COLLATION mycollation2 (provider = icu,locale = 'fr');

</programlisting>

</para>

</sect3>

<sect3 id="icu-canonicalization">

<title>Locale Canonicalization and Validation</title>

<para>

language tag if not already in that form. For instance,

<screen>

CREATE COLLATION mycollation3 (PROVIDER = icu,LOCALE = 'en-US-u-kn-true');

CREATE COLLATION mycollation3 (provider = icu,locale = 'en-US-u-kn-true');

NOTICE: using standard form "en-US-u-kn" for locale "en-US-u-kn-true"

CREATE COLLATION mycollation4 (PROVIDER = icu,LOCALE = 'de_DE.utf8');

CREATE COLLATION mycollation4 (provider = icu,locale = 'de_DE.utf8');

NOTICE: using standard form "de-DE" for locale "de_DE.utf8"

</screen>

If you see this notice, ensure that the <symbol>PROVIDER</symbol> and

<symbol>LOCALE</symbol> are the expected result. For consistent results

If you see this notice, ensure that the <symbol>provider</symbol> and

<symbol>locale</symbol> are the expected result. For consistent results

when using the ICU provider, specify the canonical <link

linkend="icu-language-tag">language tag</link> instead of relying on the

transformation.

the following warning:

<screen>

CREATE COLLATION nonsense (PROVIDER = icu,LOCALE = 'nonsense');

CREATE COLLATION nonsense (provider = icu,locale = 'nonsense');

WARNING: ICU locale "nonsense" has unknown language "nonsense"

HINT: To disable ICU locale validation, set parameter icu_validation_level to DISABLED.

CREATE COLLATION

still be created, but the behavior may not be what the user intended.

</para>

</sect3>

<sect3 id="icu-language-tag">

<title>Language Tag</title>

<para>

of digits as a single number:

<screen>

CREATE COLLATION mycollation5 (PROVIDER = icu,DETERMINISTIC = false,LOCALE = 'en-US-u-kn-ks-level2');

CREATE COLLATION mycollation5 (provider = icu,deterministic = false,locale = 'en-US-u-kn-ks-level2');

SELECT 'aB' = 'Ab' COLLATE mycollation5 as result;

result

--------

<programlisting>

-- ignore differences in accents and case

CREATE COLLATION ignore_accent_case (PROVIDER = icu,DETERMINISTIC = false,LOCALE = 'und-u-ks-level1');

CREATE COLLATION ignore_accent_case (provider = icu,deterministic = false,locale = 'und-u-ks-level1');

SELECT 'Å' = 'A' COLLATE ignore_accent_case; -- true

SELECT 'z' = 'Z' COLLATE ignore_accent_case; -- true

-- upper case letters sort before lower case.

CREATE COLLATION upper_first (PROVIDER=icu,LOCALE = 'und-u-kf-upper');

CREATE COLLATION upper_first (provider =icu,locale = 'und-u-kf-upper');

SELECT 'B' &lt; 'b' COLLATE upper_first; -- true

-- treat digits numerically and ignore punctuation

CREATE COLLATION num_ignore_punct (PROVIDER = icu,DETERMINISTIC = false,LOCALE = 'und-u-ka-shifted-kn');

CREATE COLLATION num_ignore_punct (provider = icu,deterministic = false,locale = 'und-u-ka-shifted-kn');

SELECT 'id-45' &lt; 'id-123' COLLATE num_ignore_punct; -- true

SELECT 'w;x*y-z' = 'wxyz' COLLATE num_ignore_punct; -- true

</programlisting>

linkend="icu-collation-settings-table">collation settings</link>. Higher

levels correspond to finer textual features.

</para>

<para>

<xref linkend="icu-collation-levels"/> shows which textual feature

differences are considered significant when determining equality at the

given level. The unicode character <literal>U+2063</literal> is an

invisible separator, and as seen in the table, is ignored for at all

levels of comparison less than <literal>identic</literal>.

</para>

<para>

<table id="icu-collation-levels">

<title>ICU Collation Levels</title>

</tgroup>

</table>

The above table shows which textual feature differences are

considered significant when determining equality at the given level. The

unicode character <literal>U+2063</literal> is an invisible separator,

and as seen in the table, is ignored for at all levels of comparison less

than <literal>identic</literal>.

</para>

<para>

At every level, even with full normalization off, basic normalization is

performed. For example, <literal>'á'</literal> may be composed of the

code points <literal>U&amp;'\0061\0301'</literal> or the single code

point <literal>U&amp;'\00E1'</literal>, and those sequences will be

considered equal even at the <literal>identic</literal> level. To treat

any difference in code point representation as distinct, use a collation

created with <symbol>DETERMINISTIC</symbol> set to

created with <symbol>deterministic</symbol> set to

<literal>true</literal>.

</para>

<sect4 id="icu-collation-level-examples">

<title>Collation Level Examples</title>

<para>

<programlisting>

CREATE COLLATION level3 (PROVIDER=icu,DETERMINISTIC=false,LOCALE='und-u-ka-shifted-ks-level3');

CREATE COLLATION level4 (PROVIDER=icu,DETERMINISTIC=false,LOCALE='und-u-ka-shifted-ks-level4');

CREATE COLLATION identic (PROVIDER=icu,DETERMINISTIC=false,LOCALE='und-u-ka-shifted-ks-identic');

CREATE COLLATION level3 (provider =icu,deterministic =false,locale ='und-u-ka-shifted-ks-level3');

CREATE COLLATION level4 (provider =icu,deterministic =false,locale ='und-u-ka-shifted-ks-level4');

CREATE COLLATION identic (provider =icu,deterministic =false,locale ='und-u-ka-shifted-ks-identic');

-- invisible separator ignored at all levels except identic

SELECT 'ab' = U&amp;'a\2063b' COLLATE level4; -- true

</para>

</sect4>

</sect3>

<sect3 id="icu-collation-settings">

<title>Collation Settings for an ICU Locale</title>

<para>

<xref linkend="icu-collation-settings-table"/> shows the available

collation settings, which can be used as part of a language tag to

customize a collation.

</para>

<para>

<table id="icu-collation-settings-table">

<title>ICU Collation Settings</title>

</thead>

<tbody>

<row>

<entry><literal>ks</literal></entry>

<entry><literal>level1</literal>, <literal>level2</literal>, <literal>level3</literal>, <literal>level4</literal>, <literal>identic</literal></entry>

<entry><literal>level3</literal></entry>

<entry><literal>co</literal></entry>

<entry><literal>emoji</literal>, <literal>phonebk</literal>, <literal>standard</literal>, <replaceable>...</replaceable></entry>

<entry><literal>standard</literal></entry>

<entry>

Sensitivity (or "strength") when determining equality, with

<literal>level1</literal> the least sensitive to differences and

<literal>identic</literal> the most sensitive to differences. See

<xref linkend="icu-collation-levels"/> for details.

Collation type. See <xref linkend="icu-external-references"/> for additional options and details.

</entry>

</row>

<row>

before <literal>'aé'</literal>.

</entry>

</row>

<row>

<entry><literal>kk</literal></entry>

<entry><literal>true</literal>, <literal>false</literal></entry>

<entry><literal>false</literal></entry>

<entry>

<para>

Enable full normalization; may affect performance. Basic

normalization is performed even when set to

<literal>false</literal>. Locales for languages that require full

normalization typically enable it by default.

</para>

<para>

Full normalization is important in some cases, such as when

multiple accents are applied to a single character. For example,

the code point sequences <literal>U&amp;'\0065\0323\0302'</literal>

and <literal>U&amp;'\0065\0302\0323'</literal> represent

an <literal>e</literal> with circumflex and dot-below accents

applied in different orders. With full normalization

on, these code point sequences are treated as equal; otherwise they

are unequal.

</para>

</entry>

</row>

<row>

<entry><literal>kc</literal></entry>

<entry><literal>true</literal>, <literal>false</literal></entry>

<literal>'id-123'</literal>.

</entry>

</row>

<row>

<entry><literal>kk</literal></entry>

<entry><literal>true</literal>, <literal>false</literal></entry>

<entry><literal>false</literal></entry>

<entry>

<para>

Enable full normalization; may affect performance. Basic

normalization is performed even when set to

<literal>false</literal>. Locales for languages that require full

normalization typically enable it by default.

</para>

<para>

Full normalization is important in some cases, such as when

multiple accents are applied to a single character. For example,

the code point sequences <literal>U&amp;'\0065\0323\0302'</literal>

and <literal>U&amp;'\0065\0302\0323'</literal> represent

an <literal>e</literal> with circumflex and dot-below accents

applied in different orders. With full normalization

on, these code point sequences are treated as equal; otherwise they

are unequal.

</para>

</entry>

</row>

<row>

<entry><literal>kr</literal></entry>

<entry>

</para>

</entry>

</row>

<row>

<entry><literal>ks</literal></entry>

<entry><literal>level1</literal>, <literal>level2</literal>, <literal>level3</literal>, <literal>level4</literal>, <literal>identic</literal></entry>

<entry><literal>level3</literal></entry>

<entry>

Sensitivity (or "strength") when determining equality, with

<literal>level1</literal> the least sensitive to differences and

<literal>identic</literal> the most sensitive to differences. See

<xref linkend="icu-collation-levels"/> for details.

</entry>

</row>

<row>

<entry><literal>kv</literal></entry>

<entry>

to <literal>level3</literal> or lower to take effect.

</entry>

</row>

<row>

<entry><literal>co</literal></entry>

<entry><literal>emoji</literal>, <literal>phonebk</literal>, <literal>standard</literal>, <replaceable>...</replaceable></entry>

<entry><literal>standard</literal></entry>

<entry>

Collation type. See <xref linkend="icu-external-references"/> for additional options and details.

</entry>

</row>

</tbody>

</tgroup>

</table>

<note>

<para>

For many collation settings, you must create the collation with

<option>DETERMINISTIC</option> set to <literal>false</literal> for the

<option>deterministic</option> set to <literal>false</literal> for the

setting to have the desired effect (see <xref

linkend="collation-nondeterministic"/>). Additionally, some settings

only take effect when the key <literal>ka</literal> is set to

</para>

</note>

</sect3>

<sect3 id="icu-locale-examples">

<title>Examples</title>

<para>

</variablelist>

</para>

</sect3>

<sect3 id="icu-external-references">

<title>External References for ICU</title>

<para>