diff options
Diffstat (limited to 'doc/src/sgml/html/fuzzystrmatch.html')
| -rw-r--r-- | doc/src/sgml/html/fuzzystrmatch.html | 138 |
1 files changed, 138 insertions, 0 deletions
diff --git a/doc/src/sgml/html/fuzzystrmatch.html b/doc/src/sgml/html/fuzzystrmatch.html new file mode 100644 index 0000000..8b50d05 --- /dev/null +++ b/doc/src/sgml/html/fuzzystrmatch.html @@ -0,0 +1,138 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>F.15. fuzzystrmatch</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="file-fdw.html" title="F.14. file_fdw" /><link rel="next" href="hstore.html" title="F.16. hstore" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.15. fuzzystrmatch</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="file-fdw.html" title="F.14. file_fdw">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 14.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="hstore.html" title="F.16. hstore">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="FUZZYSTRMATCH"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.15. fuzzystrmatch</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="fuzzystrmatch.html#id-1.11.7.24.6">F.15.1. Soundex</a></span></dt><dt><span class="sect2"><a href="fuzzystrmatch.html#id-1.11.7.24.7">F.15.2. Levenshtein</a></span></dt><dt><span class="sect2"><a href="fuzzystrmatch.html#id-1.11.7.24.8">F.15.3. Metaphone</a></span></dt><dt><span class="sect2"><a href="fuzzystrmatch.html#id-1.11.7.24.9">F.15.4. Double Metaphone</a></span></dt></dl></div><a id="id-1.11.7.24.2" class="indexterm"></a><p> + The <code class="filename">fuzzystrmatch</code> module provides several + functions to determine similarities and distance between strings. + </p><div class="caution"><h3 class="title">Caution</h3><p> + At present, the <code class="function">soundex</code>, <code class="function">metaphone</code>, + <code class="function">dmetaphone</code>, and <code class="function">dmetaphone_alt</code> functions do + not work well with multibyte encodings (such as UTF-8). + </p></div><p> + This module is considered <span class="quote">“<span class="quote">trusted</span>”</span>, that is, it can be + installed by non-superusers who have <code class="literal">CREATE</code> privilege + on the current database. + </p><div class="sect2" id="id-1.11.7.24.6"><div class="titlepage"><div><div><h3 class="title">F.15.1. Soundex</h3></div></div></div><p> + The Soundex system is a method of matching similar-sounding names + by converting them to the same code. It was initially used by the + United States Census in 1880, 1900, and 1910. Note that Soundex + is not very useful for non-English names. + </p><p> + The <code class="filename">fuzzystrmatch</code> module provides two functions + for working with Soundex codes: + </p><a id="id-1.11.7.24.6.4" class="indexterm"></a><a id="id-1.11.7.24.6.5" class="indexterm"></a><pre class="synopsis"> +soundex(text) returns text +difference(text, text) returns int +</pre><p> + The <code class="function">soundex</code> function converts a string to its Soundex code. + The <code class="function">difference</code> function converts two strings to their Soundex + codes and then reports the number of matching code positions. Since + Soundex codes have four characters, the result ranges from zero to four, + with zero being no match and four being an exact match. (Thus, the + function is misnamed — <code class="function">similarity</code> would have been + a better name.) + </p><p> + Here are some usage examples: + </p><pre class="programlisting"> +SELECT soundex('hello world!'); + +SELECT soundex('Anne'), soundex('Ann'), difference('Anne', 'Ann'); +SELECT soundex('Anne'), soundex('Andrew'), difference('Anne', 'Andrew'); +SELECT soundex('Anne'), soundex('Margaret'), difference('Anne', 'Margaret'); + +CREATE TABLE s (nm text); + +INSERT INTO s VALUES ('john'); +INSERT INTO s VALUES ('joan'); +INSERT INTO s VALUES ('wobbly'); +INSERT INTO s VALUES ('jack'); + +SELECT * FROM s WHERE soundex(nm) = soundex('john'); + +SELECT * FROM s WHERE difference(s.nm, 'john') > 2; +</pre></div><div class="sect2" id="id-1.11.7.24.7"><div class="titlepage"><div><div><h3 class="title">F.15.2. Levenshtein</h3></div></div></div><p> + This function calculates the Levenshtein distance between two strings: + </p><a id="id-1.11.7.24.7.3" class="indexterm"></a><a id="id-1.11.7.24.7.4" class="indexterm"></a><pre class="synopsis"> +levenshtein(text source, text target, int ins_cost, int del_cost, int sub_cost) returns int +levenshtein(text source, text target) returns int +levenshtein_less_equal(text source, text target, int ins_cost, int del_cost, int sub_cost, int max_d) returns int +levenshtein_less_equal(text source, text target, int max_d) returns int +</pre><p> + Both <code class="literal">source</code> and <code class="literal">target</code> can be any + non-null string, with a maximum of 255 characters. The cost parameters + specify how much to charge for a character insertion, deletion, or + substitution, respectively. You can omit the cost parameters, as in + the second version of the function; in that case they all default to 1. + </p><p> + <code class="function">levenshtein_less_equal</code> is an accelerated version of the + Levenshtein function for use when only small distances are of interest. + If the actual distance is less than or equal to <code class="literal">max_d</code>, + then <code class="function">levenshtein_less_equal</code> returns the correct + distance; otherwise it returns some value greater than <code class="literal">max_d</code>. + If <code class="literal">max_d</code> is negative then the behavior is the same as + <code class="function">levenshtein</code>. + </p><p> + Examples: + </p><pre class="screen"> +test=# SELECT levenshtein('GUMBO', 'GAMBOL'); + levenshtein +------------- + 2 +(1 row) + +test=# SELECT levenshtein('GUMBO', 'GAMBOL', 2, 1, 1); + levenshtein +------------- + 3 +(1 row) + +test=# SELECT levenshtein_less_equal('extensive', 'exhaustive', 2); + levenshtein_less_equal +------------------------ + 3 +(1 row) + +test=# SELECT levenshtein_less_equal('extensive', 'exhaustive', 4); + levenshtein_less_equal +------------------------ + 4 +(1 row) +</pre></div><div class="sect2" id="id-1.11.7.24.8"><div class="titlepage"><div><div><h3 class="title">F.15.3. Metaphone</h3></div></div></div><p> + Metaphone, like Soundex, is based on the idea of constructing a + representative code for an input string. Two strings are then + deemed similar if they have the same codes. + </p><p> + This function calculates the metaphone code of an input string: + </p><a id="id-1.11.7.24.8.4" class="indexterm"></a><pre class="synopsis"> +metaphone(text source, int max_output_length) returns text +</pre><p> + <code class="literal">source</code> has to be a non-null string with a maximum of + 255 characters. <code class="literal">max_output_length</code> sets the maximum + length of the output metaphone code; if longer, the output is truncated + to this length. + </p><p> + Example: + </p><pre class="screen"> +test=# SELECT metaphone('GUMBO', 4); + metaphone +----------- + KM +(1 row) +</pre></div><div class="sect2" id="id-1.11.7.24.9"><div class="titlepage"><div><div><h3 class="title">F.15.4. Double Metaphone</h3></div></div></div><p> + The Double Metaphone system computes two <span class="quote">“<span class="quote">sounds like</span>”</span> strings + for a given input string — a <span class="quote">“<span class="quote">primary</span>”</span> and an + <span class="quote">“<span class="quote">alternate</span>”</span>. In most cases they are the same, but for non-English + names especially they can be a bit different, depending on pronunciation. + These functions compute the primary and alternate codes: + </p><a id="id-1.11.7.24.9.3" class="indexterm"></a><a id="id-1.11.7.24.9.4" class="indexterm"></a><pre class="synopsis"> +dmetaphone(text source) returns text +dmetaphone_alt(text source) returns text +</pre><p> + There is no length limit on the input strings. + </p><p> + Example: + </p><pre class="screen"> +test=# SELECT dmetaphone('gumbo'); + dmetaphone +------------ + KMP +(1 row) +</pre></div></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="file-fdw.html" title="F.14. file_fdw">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="hstore.html" title="F.16. hstore">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.14. file_fdw </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 14.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> F.16. hstore</td></tr></table></div></body></html>
\ No newline at end of file |