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Add word_similarity to pg_trgm contrib module.

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Patch introduces a concept of similarity over string and just a word from
another string.

Version of extension is not changed because 1.2 was already introduced in 9.6
release cycle, so, there wasn't a public version.

Author: Alexander Korotkov, Artur Zakirov
This commit is contained in:
Teodor Sigaev
2016-03-16 18:59:21 +03:00
parent 1c4f001b79
commit f576b17cd6
10 changed files with 726 additions and 75 deletions
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79
doc/src/sgml/pgtrgm.sgml
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@ -92,6 +92,21 @@
(In practice this is seldom useful except for debugging.)
</entry>
</row>
<row>
<entry>
<function>word_similarity(text, text)</function>
<indexterm><primary>word_similarity</primary></indexterm>
</entry>
<entry><type>real</type></entry>
<entry>
Returns a number that indicates how similar the first string
to the most similar word of the second string. The function searches in
the second string a most similar word not a most similar substring. The
range of the result is zero (indicating that the two strings are
completely dissimilar) to one (indicating that the first string is
identical to one of the word of the second string).
</entry>
</row>
<row>
<entry><function>show_limit()</function><indexterm><primary>show_limit</primary></indexterm></entry>
<entry><type>real</type></entry>
@ -137,6 +152,16 @@
<varname>pg_trgm.similarity_threshold</>.
</entry>
</row>
<row>
<entry><type>text</> <literal>%&gt;</literal> <type>text</></entry>
<entry><type>boolean</type></entry>
<entry>
Returns <literal>true</> if its first argument has the similar word in
the second argument and they have a similarity that is greater than the
current word similarity threshold set by
<varname>pg_trgm.word_similarity_threshold</> parameter.
</entry>
</row>
<row>
<entry><type>text</> <literal>&lt;-&gt;</literal> <type>text</></entry>
<entry><type>real</type></entry>
@ -145,6 +170,16 @@
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>word_similarity()</> value.
</entry>
</row>
</tbody>
</tgroup>
</table>
@ -168,6 +203,23 @@
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-pgtrgm-word-similarity-threshold" xreflabel="pg_trgm.word_similarity_threshold">
<term>
<varname>pg_trgm.word_similarity_threshold</> (<type>real</type>)
<indexterm>
<primary>
<varname>pg_trgm.word_similarity_threshold</> configuration parameter
</primary>
</indexterm>
</term>
<listitem>
<para>
Sets the current word similarity threshold that is used by
the <literal>%&gt;</> operator. The threshold must be between
0 and 1 (default is 0.6).
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
@ -225,6 +277,33 @@ SELECT t, t &lt;-&gt; '<replaceable>word</>' AS dist
a small number of the closest matches is wanted.
</para>
<para>
Also you can use an index on the <structfield>t</> column for word
similarity. For example:
<programlisting>
SELECT t, word_similarity('<replaceable>word</>', t) AS sml
FROM test_trgm
WHERE t %&gt; '<replaceable>word</>'
ORDER BY sml DESC, t;
</programlisting>
This will return all values in the text column that have a word
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