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Diffstat (limited to 'doc/src/sgml/pgtrgm.sgml')
| -rw-r--r-- | doc/src/sgml/pgtrgm.sgml | 79 |
1 files changed, 79 insertions, 0 deletions
diff --git a/doc/src/sgml/pgtrgm.sgml b/doc/src/sgml/pgtrgm.sgml index 1a9b5a796f..cdce17251f 100644 --- a/doc/src/sgml/pgtrgm.sgml +++ b/doc/src/sgml/pgtrgm.sgml @@ -93,6 +93,21 @@ </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> <entry> @@ -138,6 +153,16 @@ </entry> </row> <row> + <entry><type>text</> <literal>%></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><-></literal> <type>text</></entry> <entry><type>real</type></entry> <entry> @@ -145,6 +170,16 @@ one minus the <function>similarity()</> value. </entry> </row> + <row> + <entry> + <type>text</> <literal><->></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>%></> operator. The threshold must be between + 0 and 1 (default is 0.6). + </para> + </listitem> + </varlistentry> </variablelist> </sect2> @@ -226,6 +278,33 @@ SELECT t, t <-> '<replaceable>word</>' AS dist </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 %> '<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 <->> '<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 <programlisting> |