diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/pgtrgm.sgml | 88 |
1 files changed, 86 insertions, 2 deletions
diff --git a/doc/src/sgml/pgtrgm.sgml b/doc/src/sgml/pgtrgm.sgml index b5d893c9fbb..8f395296d8f 100644 --- a/doc/src/sgml/pgtrgm.sgml +++ b/doc/src/sgml/pgtrgm.sgml @@ -106,6 +106,17 @@ </entry> </row> <row> + <entry> + <function>strict_word_similarity(text, text)</function> + <indexterm><primary>strict_word_similarity</primary></indexterm> + </entry> + <entry><type>real</type></entry> + <entry> + Same as <function>word_similarity(text, text)</function>, but forces + extent boundaries to match word boundaries. + </entry> + </row> + <row> <entry><function>show_limit()</function><indexterm><primary>show_limit</primary></indexterm></entry> <entry><type>real</type></entry> <entry> @@ -157,6 +168,29 @@ a part of the word. </para> + <para> + At the same time, <function>strict_word_similarity(text, text)</function> + has to select an extent that matches word boundaries. In the example above, + <function>strict_word_similarity(text, text)</function> would select the + extent <literal>{" w"," wo","wor","ord","rds", ds "}</literal>, which + corresponds to the whole word <literal>'words'</literal>. + +<programlisting> +# SELECT strict_word_similarity('word', 'two words'), similarity('word', 'words'); + strict_word_similarity | similarity +------------------------+------------ + 0.571429 | 0.571429 +(1 row) +</programlisting> + </para> + + <para> + Thus, the <function>strict_word_similarity(text, text)</function> function + is useful for finding similar subsets of whole words, while + <function>word_similarity(text, text)</function> is more suitable for + searching similar parts of words. + </para> + <table id="pgtrgm-op-table"> <title><filename>pg_trgm</filename> Operators</title> <tgroup cols="3"> @@ -197,6 +231,24 @@ </entry> </row> <row> + <entry><type>text</type> <literal><<%</literal> <type>text</type></entry> + <entry><type>boolean</type></entry> + <entry> + Returns <literal>true</literal> if its second argument has a continuous + extent of an ordered trigram set that matches word boundaries, + and its similarity to the trigram set of the first argument is greater + than the current strict word similarity threshold set by the + <varname>pg_trgm.strict_word_similarity_threshold</varname> parameter. + </entry> + </row> + <row> + <entry><type>text</type> <literal>%>></literal> <type>text</type></entry> + <entry><type>boolean</type></entry> + <entry> + Commutator of the <literal><<%</literal> operator. + </entry> + </row> + <row> <entry><type>text</type> <literal><-></literal> <type>text</type></entry> <entry><type>real</type></entry> <entry> @@ -223,6 +275,25 @@ Commutator of the <literal><<-></literal> operator. </entry> </row> + <row> + <entry> + <type>text</type> <literal><<<-></literal> <type>text</type> + </entry> + <entry><type>real</type></entry> + <entry> + Returns the <quote>distance</quote> between the arguments, that is + one minus the <function>strict_word_similarity()</function> value. + </entry> + </row> + <row> + <entry> + <type>text</type> <literal><->>></literal> <type>text</type> + </entry> + <entry><type>real</type></entry> + <entry> + Commutator of the <literal><<<-></literal> operator. + </entry> + </row> </tbody> </tgroup> </table> @@ -322,13 +393,20 @@ SELECT t, t <-> '<replaceable>word</replaceable>' AS dist <para> Also you can use an index on the <structfield>t</structfield> column for word - similarity. For example: + similarity or strict word similarity. Typical queries are: <programlisting> SELECT t, word_similarity('<replaceable>word</replaceable>', t) AS sml FROM test_trgm WHERE '<replaceable>word</replaceable>' <% t ORDER BY sml DESC, t; </programlisting> + and +<programlisting> +SELECT t, strict_word_similarity('<replaceable>word</replaceable>', t) AS sml + FROM test_trgm + WHERE '<replaceable>word</replaceable>' <<% t + ORDER BY sml DESC, t; +</programlisting> This will return all values in the text column for which there is a continuous extent in the corresponding ordered trigram set that is sufficiently similar to the trigram set of <replaceable>word</replaceable>, @@ -337,12 +415,18 @@ SELECT t, word_similarity('<replaceable>word</replaceable>', t) AS sml </para> <para> - A variant of the above query is + Possible variants of the above queries are: <programlisting> SELECT t, '<replaceable>word</replaceable>' <<-> t AS dist FROM test_trgm ORDER BY dist LIMIT 10; </programlisting> + and +<programlisting> +SELECT t, '<replaceable>word</replaceable>' <<<-> t 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> |