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diff --git a/doc/src/sgml/fuzzystrmatch.sgml b/doc/src/sgml/fuzzystrmatch.sgml index 8200725b17d..1eb1ad61843 100644 --- a/doc/src/sgml/fuzzystrmatch.sgml +++ b/doc/src/sgml/fuzzystrmatch.sgml @@ -1,30 +1,51 @@ +<!-- $PostgreSQL: pgsql/doc/src/sgml/fuzzystrmatch.sgml,v 1.3 2007/12/06 04:12:10 tgl Exp $ --> <sect1 id="fuzzystrmatch"> <title>fuzzystrmatch</title> - + + <indexterm zone="fuzzystrmatch"> + <primary>fuzzystrmatch</primary> + </indexterm> + <para> - This section describes the fuzzystrmatch module which provides different + The <filename>fuzzystrmatch</> module provides several functions to determine similarities and distance between strings. </para> <sect2> <title>Soundex</title> + <para> - The Soundex system is a method of matching similar sounding names - (or any words) to the same code. It was initially used by the - United States Census in 1880, 1900, and 1910, but it has little use - beyond English names (or the English pronunciation of names), and - it is not a linguistic tool. + 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. </para> + <para> - When comparing two soundex values to determine similarity, the - difference function reports how close the match is on a scale - from zero to four, with zero being no match and four being an - exact match. + The <filename>fuzzystrmatch</> module provides two functions + for working with Soundex codes: </para> + + <programlisting> + soundex(text) returns text + difference(text, text) returns int + </programlisting> + + <para> + The <function>soundex</> function converts a string to its Soundex code. + The <function>difference</> 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 — <function>similarity</> would have been + a better name.) + </para> + <para> - The following are some usage examples: + Here are some usage examples: </para> + <programlisting> SELECT soundex('hello world!'); @@ -41,81 +62,106 @@ INSERT INTO s VALUES ('jack'); SELECT * FROM s WHERE soundex(nm) = soundex('john'); -SELECT a.nm, b.nm FROM s a, s b WHERE soundex(a.nm) = soundex(b.nm) AND a.oid <> b.oid; - -CREATE FUNCTION text_sx_eq(text, text) RETURNS boolean AS -'select soundex($1) = soundex($2)' -LANGUAGE SQL; - -CREATE FUNCTION text_sx_lt(text, text) RETURNS boolean AS -'select soundex($1) < soundex($2)' -LANGUAGE SQL; - -CREATE FUNCTION text_sx_gt(text, text) RETURNS boolean AS -'select soundex($1) > soundex($2)' -LANGUAGE SQL; - -CREATE FUNCTION text_sx_le(text, text) RETURNS boolean AS -'select soundex($1) <= soundex($2)' -LANGUAGE SQL; - -CREATE FUNCTION text_sx_ge(text, text) RETURNS boolean AS -'select soundex($1) >= soundex($2)' -LANGUAGE SQL; +SELECT * FROM s WHERE difference(s.nm, 'john') > 2; + </programlisting> + </sect2> -CREATE FUNCTION text_sx_ne(text, text) RETURNS boolean AS -'select soundex($1) <> soundex($2)' -LANGUAGE SQL; + <sect2> + <title>Levenshtein</title> -DROP OPERATOR #= (text, text); + <para> + This function calculates the Levenshtein distance between two strings: + </para> -CREATE OPERATOR #= (leftarg=text, rightarg=text, procedure=text_sx_eq, commutator = #=); + <programlisting> + levenshtein(text source, text target) returns int + </programlisting> -SELECT * FROM s WHERE text_sx_eq(nm, 'john'); + <para> + Both <literal>source</literal> and <literal>target</literal> can be any + non-null string, with a maximum of 255 characters. + </para> -SELECT * FROM s WHERE s.nm #= 'john'; + <para> + Example: + </para> -SELECT * FROM s WHERE difference(s.nm, 'john') > 2; + <programlisting> +test=# SELECT levenshtein('GUMBO', 'GAMBOL'); + levenshtein +------------- + 2 +(1 row) </programlisting> </sect2> <sect2> - <title>levenshtein</title> + <title>Metaphone</title> + + <para> + 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. + </para> + <para> - This function calculates the levenshtein distance between two strings: + This function calculates the metaphone code of an input string: </para> + <programlisting> - int levenshtein(text source, text target) + metaphone(text source, int max_output_length) returns text </programlisting> + <para> - Both <literal>source</literal> and <literal>target</literal> can be any - NOT NULL string with a maximum of 255 characters. + <literal>source</literal> has to be a non-null string with a maximum of + 255 characters. <literal>max_output_length</literal> sets the maximum + length of the output metaphone code; if longer, the output is truncated + to this length. </para> + <para> Example: </para> + <programlisting> - SELECT levenshtein('GUMBO','GAMBOL'); +test=# SELECT metaphone('GUMBO', 4); + metaphone +----------- + KM +(1 row) </programlisting> </sect2> <sect2> - <title>metaphone</title> + <title>Double Metaphone</title> + <para> - This function calculates and returns the metaphone code of an input string: + The Double Metaphone system computes two <quote>sounds like</> strings + for a given input string — a <quote>primary</> and an + <quote>alternate</>. 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: </para> + <programlisting> - text metahpone(text source, int max_output_length) + dmetaphone(text source) returns text + dmetaphone_alt(text source) returns text </programlisting> + <para> - <literal>source</literal> has to be a NOT NULL string with a maximum of - 255 characters. <literal>max_output_length</literal> fixes the maximum - length of the output metaphone code; if longer, the output is truncated - to this length. + There is no length limit on the input strings. + </para> + + <para> + Example: </para> - <para>Example</para> + <programlisting> - SELECT metaphone('GUMBO',4); +test=# select dmetaphone('gumbo'); + dmetaphone +------------ + KMP +(1 row) </programlisting> </sect2> |