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提交 b2c5de61 编写于 作者: L Lisa Owen 提交者： David Yozie
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docs - revisit fuzzystrmatch module doc contents (#7327)

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gpdb-doc/dita/ref_guide/modules/fuzzystrmatch.xml
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<body>
<p>The <codeph>fuzzystrmatch</codeph> module provides functions to determine
similarities and distance between strings based on various algorithms.</p>
<ul id="ul_ltl_rym_hp">
<li>
<xref href="#topic_soundex" format="dita"/>
</li>
<li>
<xref href="#topic_levenshtein" format="dita"/>
</li>
<li>
<xref href="#topic_metaphone" format="dita"/>
</li>
<li>
<xref href="#d_metaphone" format="dita"/>
</li>
<li>
<xref href="#topic_install" format="dita"/>
</li>
</ul>
<p>The Greenplum Database installation contains the files required for the functions in this
module and SQL scripts to define the module functions in a database and remove
the functions from a database. </p>
<note type="warning">The functions <apiname>soundex</apiname>, <apiname>metaphone</apiname>,
<apiname>dmetaphone</apiname>, and <apiname>dmetaphone_alt</apiname> do not work well with
multibyte encodings (such as UTF-8).</note>
<p>The Greenplum Database Fuzzy String Match is based on the PostgreSQL
fuzzystrmatch module.</p>
<p>The Greenplum Database <codeph>fuzzystrmatch</codeph> module is equivalent
to the PostgreSQL <codeph>fuzzystrmatch</codeph> module. There are no
Greenplum Database or MPP-specific considerations for the module.</p>
</body>
<topic id="topic_soundex">
<title>Soundex Functions</title>
<topic id="topic_reg">
<title>Installing and Registering the Module</title>
<body>
<p>The Soundex system is a method of matching similar-sounding (similar phonemes) names by
converting them to the same code.</p>
<note>Soundex is most useful for English names.</note>
<p>These functions work with Soundex codes:</p>
<codeblock>soundex(text <varname>string1</varname>) returns text
difference(text <varname>string1</varname>, text <varname>string2</varname>) returns int</codeblock>
<p>The <apiname>soundex</apiname> function converts a string to its Soundex code. Soundex
codes consist of four characters.</p>
<p>The <apiname>difference</apiname> function converts two strings to their Soundex codes
and then reports the number of matching code positions. The result ranges from zero to
four, zero being no match and four being an exact match. These are some examples:</p>
<codeblock>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;</codeblock>
<p>For information about the Soundex indexing system see <xref
href="https://www.archives.gov/research/census/soundex.html" format="html"
scope="external"/>. </p>
<p>The <codeph>fuzzystrmatch</codeph> module is installed when you install
Greenplum Database. Before you can use any of the functions defined in the
module, you must register the <codeph>fuzzystrmatch</codeph> extension in
each database in which you want to use the functions.
<ph otherprops="pivotal">Refer to <xref href="../../install_guide/install_modules.xml"
format="dita" scope="peer">Installing Additional Supplied Modules</xref>
for more information.</ph></p>
</body>
</topic>
<topic id="topic_levenshtein">
<title>Levenshtein Functions</title>
<topic id="topic_info">
<title>Module Documentation</title>
<body>
<p>These functions calculate the Levenshtein distance between two strings: </p>
<codeblock>levenshtein(text <varname>source</varname>, text <varname>target</varname>, int <varname>ins_cost</varname>, int <varname>del_cost</varname>, int <varname>sub_cost</varname>) returns int
levenshtein(text <varname>source</varname>, text <varname>target</varname>) returns int
levenshtein_less_equal(text <varname>source</varname>, text <varname>target</varname>, int <varname>ins_cost</varname>, int <varname>del_cost</varname>, int <varname>sub_cost</varname>, int <varname>max_d</varname>) returns int
levenshtein_less_equal(text <varname>source</varname>, text <varname>target</varname>, int max_d) returns int</codeblock>
<p>Both the <codeph>source</codeph> and <codeph>target</codeph> parameters can be any
non-null string, with a maximum of 255 bytes. The cost parameters
<codeph>ins_cost</codeph>, <codeph>del_cost</codeph>, and <codeph>sub_cost</codeph>
specify cost of a character insertion, deletion, or substitution, respectively. You can
omit the cost parameters, as in the second version of the function; in that case the cost
parameters default to 1.</p>
<p>
<apiname>levenshtein_less_equal</apiname> is accelerated version of
<apiname>levenshtein</apiname> function for low values of distance. If actual distance
is less or equal then <codeph>max_d</codeph>, then
<apiname>levenshtein_less_equal</apiname> returns an accurate value of the distance.
Otherwise, this function returns value which is greater than <codeph>max_d</codeph>.
Examples:</p>
<codeblock>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)</codeblock>
<p>For information about the Levenshtein algorithm, see <xref
href="http://www.levenshtein.net/" format="html" scope="external"/>.</p>
</body>
</topic>
<topic id="topic_metaphone">
<title>Metaphone Functions</title>
<body>
<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. This
function calculates the metaphone code of an input string
:<codeblock>metaphone(text <varname>source</varname>, int <varname>max_output_length</varname>) returns text</codeblock></p>
<p>The <codeph>source</codeph> parameter must be a non-null string with a maximum of 255
characters. The <codeph>max_output_length</codeph> parameter sets the maximum length of
the output metaphone code; if longer, the output is truncated to this length. Example:</p>
<codeblock>test=# SELECT metaphone('GUMBO', 4);
metaphone
-----------
KM
(1 row)</codeblock>
<p>For information about the Metaphone algorithm, see <xref
href="https://en.wikipedia.org/wiki/Metaphone" format="html" scope="external"/>.</p>
</body>
</topic>
<topic id="d_metaphone">
<title>Double Metaphone Functions</title>
<body>
<p>The Double Metaphone system computes two "sounds like" strings for a given input string -
a "primary" and an "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:<codeblock>dmetaphone(text <varname>source</varname>) returns text
dmetaphone_alt(text <varname>source</varname>) returns text</codeblock>
There is no length limit on the input strings. Example:</p>
<codeblock>test=# select dmetaphone('gumbo');
dmetaphone
------------
KMP
(1 row)</codeblock>
<p>For information about the Double Metaphone algorithm, see <xref
href="https://en.wikipedia.org/wiki/Metaphone#Double_Metaphone" format="html"
scope="external"/>.</p>
</body>
</topic>
<topic id="topic_install">
<title>Registering the fuzzystrmatch Functions</title>
<body>
<p>Greenplum Database supplies SQL scripts to register the <codeph>fuzzystrmatch</codeph>
module functions.</p>
<p>Before you can use <codeph>fuzzystrmatch</codeph> functions, you must register
the <codeph>fuzzystrmatch</codeph> extension in each database in which you want
to use the functions:</p>
<codeblock>psql -d testdb -c "CREATE EXTENSION fuzzystrmatch"</codeblock>
<p>To remove the functions from a database:</p>
<codeblock>psql -d testdb -c "DROP EXTENSION fuzzystrmatch"</codeblock>
<note>When you remove the <codeph>fuzzystrmatch</codeph>functions from a database,
UDFs that you created in the database that use the functions will no longer
work.</note>
<p>See <xref href="https://www.postgresql.org/docs/9.4/fuzzystrmatch.html"
format="html" scope="external">fuzzystrmatch</xref> in the PostgreSQL
documentation for detailed information about the individual functions in
this module.</p>
</body>
</topic>
</topic>
......
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