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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >fuzzystrmatch</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 9.2.24 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Additional Supplied Modules" HREF="contrib.html"><LINK REL="PREVIOUS" TITLE="file_fdw" HREF="file-fdw.html"><LINK REL="NEXT" TITLE="hstore" HREF="hstore.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2017-11-06T22:43:11"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.2.24 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="file_fdw" HREF="file-fdw.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="contrib.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Appendix F. Additional Supplied Modules</TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="hstore" HREF="hstore.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="FUZZYSTRMATCH" >F.15. fuzzystrmatch</A ></H1 ><P > The <TT CLASS="FILENAME" >fuzzystrmatch</TT > module provides several functions to determine similarities and distance between strings. </P ><DIV CLASS="CAUTION" ><P ></P ><TABLE CLASS="CAUTION" BORDER="1" WIDTH="100%" ><TR ><TD ALIGN="CENTER" ><B >Caution</B ></TD ></TR ><TR ><TD ALIGN="LEFT" ><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 ></TD ></TR ></TABLE ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="AEN148289" >F.15.1. Soundex</A ></H2 ><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 <TT CLASS="FILENAME" >fuzzystrmatch</TT > module provides two functions for working with Soundex codes: </P ><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" ><H2 CLASS="SECT2" ><A NAME="AEN148301" >F.15.2. Levenshtein</A ></H2 ><P > This function calculates the Levenshtein distance between two strings: </P ><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 <TT CLASS="LITERAL" >source</TT > and <TT CLASS="LITERAL" >target</TT > can be any non-null string, with a maximum of 255 bytes. 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. <TT CLASS="LITERAL" >levenshtein_less_equal</TT > is accelerated version of levenshtein function for low values of distance. If actual distance is less or equal then max_d, then <TT CLASS="LITERAL" >levenshtein_less_equal</TT > returns accurate value of it. Otherwise this function returns value which is greater than max_d. </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" ><H2 CLASS="SECT2" ><A NAME="AEN148312" >F.15.3. Metaphone</A ></H2 ><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 ><PRE CLASS="SYNOPSIS" >metaphone(text source, int max_output_length) returns text</PRE ><P > <TT CLASS="LITERAL" >source</TT > has to be a non-null string with a maximum of 255 characters. <TT CLASS="LITERAL" >max_output_length</TT > 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" ><H2 CLASS="SECT2" ><A NAME="AEN148322" >F.15.4. Double Metaphone</A ></H2 ><P > The Double Metaphone system computes two <SPAN CLASS="QUOTE" >"sounds like"</SPAN > strings for a given input string — a <SPAN CLASS="QUOTE" >"primary"</SPAN > and an <SPAN CLASS="QUOTE" >"alternate"</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 ><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 CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="file-fdw.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="hstore.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >file_fdw</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="contrib.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >hstore</TD ></TR ></TABLE ></DIV ></BODY ></HTML >