</entry>

</row>

<row>

<entry><function>substring_similarity(text, text)</function><indexterm><primary>substring_similarity</primary></indexterm></entry>

<entry><function>subword_similarity(text, text)</function><indexterm><primary>subword_similarity</primary></indexterm></entry>

<entry><type>real</type></entry>

<entry>

Returns a number that indicates how similar the first string

to the most similarsubstring of the second string. The range of

to the most similarword of the second string. The range of

the result is zero (indicating that the two strings are completely

dissimilar) to one (indicating that the first string is identical

tosubstring of the secondsubstring).

toone of theword of thesecondstring).

</entry>

</row>

<row>

<entry>

Returns <literal>true</> if its arguments have a similarity that is

greater than the current similarity threshold set by

<varname>pg_trgm.limit</>.

<varname>pg_trgm.sml_limit</>.

</entry>

</row>

<row>

<entry><type>text</> <literal>&lt;%</literal> <type>text</></entry>

<entry><type>text</> <literal>%&gt;</literal> <type>text</></entry>

<entry><type>boolean</type></entry>

<entry>

Returns <literal>true</> if its arguments have asubstring similarity

that is greater than the currentsubstring similarity threshold set by

<varname>pg_trgm.substring_limit</> parameter.

Returns <literal>true</> if its arguments have asubword similarity

that is greater than the currentsubword similarity threshold set by

<varname>pg_trgm.subword_limit</> parameter.

</entry>

</row>

<row>

one minus the <function>similarity()</> value.

</entry>

</row>

<row>

<entry><type>text</> <literal>&lt;-&gt;&gt;</literal> <type>text</></entry>

<entry><type>real</type></entry>

<entry>

Returns the <quote>distance</> between the arguments, that is

one minus the <function>subword_similarity()</> value.

</entry>

</row>

</tbody>

</tgroup>

</table>

<title>GUC Parameters</title>

<variablelist>

<varlistentry id="guc-pgtrgm-limit" xreflabel="pg_trgm.limit">

<varlistentry id="guc-pgtrgm-sml-limit" xreflabel="pg_trgm.sml_limit">

<term>

<varname>pg_trgm.limit</> (<type>real</type>)

<varname>pg_trgm.sml_limit</> (<type>real</type>)

<indexterm>

<primary><varname>pg_trgm.limit</> configuration parameter</primary>

<primary><varname>pg_trgm.sml_limit</> configuration parameter</primary>

</indexterm>

</term>

<listitem>

</listitem>

</varlistentry>

<varlistentry id="guc-pgtrgm-substring-limit" xreflabel="pg_trgm.substring_limit">

<varlistentry id="guc-pgtrgm-subword-limit" xreflabel="pg_trgm.subword_limit">

<term>

<varname>pg_trgm.substring_limit</> (<type>real</type>)

<varname>pg_trgm.subword_limit</> (<type>real</type>)

<indexterm>

<primary><varname>pg_trgm.substring_limit</> configuration parameter</primary>

<primary><varname>pg_trgm.subword_limit</> configuration parameter</primary>

</indexterm>

</term>

<listitem>

<para>

Sets the currentsubstring similarity threshold that is used by

the <literal>&lt;%</> operator. The threshold must be between

Sets the currentsubword similarity threshold that is used by

the <literal>%&gt;</> operator. The threshold must be between

0 and 1 (default is 0.6).

</para>

</listitem>

</para>

<para>

Also you can use an index on the <structfield>t</> column forsubstring

Also you can use an index on the <structfield>t</> column forsubword

similarity. For example:

<programlisting>

SELECT t,substring_similarity('<replaceable>word</>', t) AS sml

SELECT t,subword_similarity('<replaceable>word</>', t) AS sml

FROM test_trgm

WHERE '<replaceable>word</>' &lt;% t

WHEREt %&gt;'<replaceable>word</>'

ORDER BY sml DESC, t;

</programlisting>

This will return all values in the text column that have asubstring

This will return all values in the text column that have aword

which sufficiently similar to <replaceable>word</>, sorted from best

match to worst. The index will be used to make this a fast operation

even over very large data sets.

</para>

<para>

A variant of the above query is

<programlisting>

SELECT t, t &lt;-&gt;&gt; '<replaceable>word</>' AS dist

FROM test_trgm

ORDER BY dist LIMIT 10;

</programlisting>

This can be implemented quite efficiently by GiST indexes, but not

by GIN indexes.

</para>

<para>

Beginning in <productname>PostgreSQL</> 9.1, these index types also support

index searches for <literal>LIKE</> and <literal>ILIKE</>, for example

</para>

</sect2>

</sect1>

</sect1>