From 55f6e5f689d3bd086fe4fdcdc823c655005e4d88 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 3 Apr 2008 21:13:07 +0000
Subject: [PATCH] Add a variant of the Levenshtein string-distance function
that lets the user specify the cost values to use, instead of always using
1's. Volkan Yazici
In passing, remove fuzzystrmatch.h, which contained a bunch of stuff that had
no business being in a .h file; fold it into its only user, fuzzystrmatch.c.
---
contrib/fuzzystrmatch/fuzzystrmatch.c | 341 +++++++++++-------
contrib/fuzzystrmatch/fuzzystrmatch.h | 171 ---------
contrib/fuzzystrmatch/fuzzystrmatch.sql.in | 6 +-
.../fuzzystrmatch/uninstall_fuzzystrmatch.sql | 4 +-
doc/src/sgml/fuzzystrmatch.sgml | 16 +-
5 files changed, 239 insertions(+), 299 deletions(-)
delete mode 100644 contrib/fuzzystrmatch/fuzzystrmatch.h
diff --git a/contrib/fuzzystrmatch/fuzzystrmatch.c b/contrib/fuzzystrmatch/fuzzystrmatch.c
index 7a6aae039fe..3d550bd8e88 100644
--- a/contrib/fuzzystrmatch/fuzzystrmatch.c
+++ b/contrib/fuzzystrmatch/fuzzystrmatch.c
@@ -5,7 +5,7 @@
*
* Joe Conway <mail@joeconway.com>
*
- * $PostgreSQL: pgsql/contrib/fuzzystrmatch/fuzzystrmatch.c,v 1.26 2008/03/25 22:42:41 tgl Exp $
+ * $PostgreSQL: pgsql/contrib/fuzzystrmatch/fuzzystrmatch.c,v 1.27 2008/04/03 21:13:07 tgl Exp $
* Copyright (c) 2001-2008, PostgreSQL Global Development Group
* ALL RIGHTS RESERVED;
*
@@ -15,6 +15,8 @@
* found at http://www.merriampark.com/ld.htm
* Also looked at levenshtein.c in the PHP 4.0.6 distribution for
* inspiration.
+ * Configurable penalty costs extension is introduced by Volkan
+ * YAZICI <volkan.yazici@gmail.com>.
*
* metaphone()
* -----------
@@ -43,153 +45,251 @@
*
*/
-#include "fuzzystrmatch.h"
+#include "postgres.h"
+
+#include <ctype.h>
+
+#include "fmgr.h"
+#include "utils/builtins.h"
PG_MODULE_MAGIC;
+
/*
- * Calculates Levenshtein Distance between two strings.
- * Uses simplest and fastest cost model only, i.e. assumes a cost of 1 for
- * each deletion, substitution, or insertion.
+ * External declarations for exported functions
*/
-PG_FUNCTION_INFO_V1(levenshtein);
-Datum
-levenshtein(PG_FUNCTION_ARGS)
+extern Datum levenshtein_with_costs(PG_FUNCTION_ARGS);
+extern Datum levenshtein(PG_FUNCTION_ARGS);
+extern Datum metaphone(PG_FUNCTION_ARGS);
+extern Datum soundex(PG_FUNCTION_ARGS);
+extern Datum difference(PG_FUNCTION_ARGS);
+
+/*
+ * Soundex
+ */
+static void _soundex(const char *instr, char *outstr);
+
+#define SOUNDEX_LEN 4
+
+/* ABCDEFGHIJKLMNOPQRSTUVWXYZ */
+static const char *soundex_table = "01230120022455012623010202";
+
+#define soundex_code(letter) soundex_table[toupper((unsigned char) (letter)) - 'A']
+
+
+/*
+ * Levenshtein
+ */
+#define MAX_LEVENSHTEIN_STRLEN 255
+
+static int levenshtein_internal(const char *s, const char *t,
+ int ins_c, int del_c, int sub_c);
+
+
+/*
+ * Metaphone
+ */
+#define MAX_METAPHONE_STRLEN 255
+
+/*
+ * Original code by Michael G Schwern starts here.
+ * Code slightly modified for use as PostgreSQL function.
+ */
+
+
+/**************************************************************************
+ metaphone -- Breaks english phrases down into their phonemes.
+
+ Input
+ word -- An english word to be phonized
+ max_phonemes -- How many phonemes to calculate. If 0, then it
+ will phonize the entire phrase.
+ phoned_word -- The final phonized word. (We'll allocate the
+ memory.)
+ Output
+ error -- A simple error flag, returns TRUE or FALSE
+
+ NOTES: ALL non-alpha characters are ignored, this includes whitespace,
+ although non-alpha characters will break up phonemes.
+****************************************************************************/
+
+
+/**************************************************************************
+ my constants -- constants I like
+
+ Probably redundant.
+
+***************************************************************************/
+
+#define META_ERROR FALSE
+#define META_SUCCESS TRUE
+#define META_FAILURE FALSE
+
+
+/* I add modifications to the traditional metaphone algorithm that you
+ might find in books. Define this if you want metaphone to behave
+ traditionally */
+#undef USE_TRADITIONAL_METAPHONE
+
+/* Special encodings */
+#define SH 'X'
+#define TH '0'
+
+static char Lookahead(char *word, int how_far);
+static int _metaphone(char *word, int max_phonemes, char **phoned_word);
+
+/* Metachar.h ... little bits about characters for metaphone */
+
+
+/*-- Character encoding array & accessing macros --*/
+/* Stolen directly out of the book... */
+char _codes[26] = {
+ 1, 16, 4, 16, 9, 2, 4, 16, 9, 2, 0, 2, 2, 2, 1, 4, 0, 2, 4, 4, 1, 0, 0, 0, 8, 0
+/* a b c d e f g h i j k l m n o p q r s t u v w x y z */
+};
+
+
+#define ENCODE(c) (isalpha((unsigned char) (c)) ? _codes[((toupper((unsigned char) (c))) - 'A')] : 0)
+
+#define isvowel(c) (ENCODE(c) & 1) /* AEIOU */
+
+/* These letters are passed through unchanged */
+#define NOCHANGE(c) (ENCODE(c) & 2) /* FJMNR */
+
+/* These form dipthongs when preceding H */
+#define AFFECTH(c) (ENCODE(c) & 4) /* CGPST */
+
+/* These make C and G soft */
+#define MAKESOFT(c) (ENCODE(c) & 8) /* EIY */
+
+/* These prevent GH from becoming F */
+#define NOGHTOF(c) (ENCODE(c) & 16) /* BDH */
+
+
+/*
+ * levenshtein_internal - Calculates Levenshtein distance metric
+ * between supplied strings. Generally
+ * (1, 1, 1) penalty costs suffices common
+ * cases, but your mileage may vary.
+ */
+static int
+levenshtein_internal(const char *s, const char *t,
+ int ins_c, int del_c, int sub_c)
{
- char *str_s = TextDatumGetCString(PG_GETARG_DATUM(0));
- char *str_t = TextDatumGetCString(PG_GETARG_DATUM(1));
- int cols = strlen(str_s) + 1;
- int rows = strlen(str_t) + 1;
- char *str_s0;
- int *u_cells;
- int *l_cells;
- int *tmp;
- int i;
- int j;
+ int m, n;
+ int *prev;
+ int *curr;
+ int i, j;
+ const char *x;
+ const char *y;
+
+ m = strlen(s);
+ n = strlen(t);
/*
- * str_s is referred to as the "source", str_t is referred to as the
- * "target", cols = length of source + 1 to allow for the initialization
- * column, rows = length of target + 1 to allow for the initialization row
+ * If either m or n is 0, the answer is the other value. This makes
+ * sense since it would take that many insertions to build a matching
+ * string
*/
+ if (!m)
+ return n;
+ if (!n)
+ return m;
/*
- * Restrict the length of the strings being compared to something
- * reasonable because we will have to perform rows * cols calculations. If
- * longer strings need to be compared, increase MAX_LEVENSHTEIN_STRLEN to
- * suit (but within your tolerance for speed and memory usage).
+ * For security concerns, restrict excessive CPU+RAM usage. (This
+ * implementation uses O(m) memory and has O(mn) complexity.)
*/
- if ((cols > MAX_LEVENSHTEIN_STRLEN + 1) || (rows > MAX_LEVENSHTEIN_STRLEN + 1))
+ if (m > MAX_LEVENSHTEIN_STRLEN ||
+ n > MAX_LEVENSHTEIN_STRLEN)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("argument exceeds the maximum length of %d bytes",
MAX_LEVENSHTEIN_STRLEN)));
- /*
- * If either rows or cols is 0, the answer is the other value. This makes
- * sense since it would take that many insertions the build a matching
- * string
- */
-
- if (cols == 0)
- PG_RETURN_INT32(rows);
-
- if (rows == 0)
- PG_RETURN_INT32(cols);
+ /* One more cell for initialization column and row. */
+ ++m;
+ ++n;
/*
- * Allocate two vectors of integers. One will be used for the "upper" row,
- * the other for the "lower" row. Initialize the "upper" row to 0..cols
+ * Instead of building an (m+1)x(n+1) array, we'll use two
+ * different arrays of size m+1 for storing accumulated values.
+ * At each step one represents the "previous" row and one is the
+ * "current" row of the notional large array.
*/
- u_cells = palloc(sizeof(int) * cols);
- for (i = 0; i < cols; i++)
- u_cells[i] = i;
+ prev = (int *) palloc(2 * m * sizeof(int));
+ curr = prev + m;
- l_cells = palloc(sizeof(int) * cols);
+ /* Initialize the "previous" row to 0..cols */
+ for (i = 0; i < m; i++)
+ prev[i] = i;
- /*
- * Use str_s0 to "rewind" the pointer to str_s in the nested for loop
- * below
- */
- str_s0 = str_s;
-
- /*
- * Loop through the rows, starting at row 1. Row 0 is used for the initial
- * "upper" row.
- */
- for (j = 1; j < rows; j++)
+ /* Loop through rows of the notional array */
+ for (y = t, j = 1; j < n; y++, j++)
{
+ int *temp;
+
/*
- * We'll always start with col 1, and initialize lower row col 0 to j
+ * First cell must increment sequentially, as we're on the
+ * j'th row of the (m+1)x(n+1) array.
*/
- l_cells[0] = j;
-
- for (i = 1; i < cols; i++)
+ curr[0] = j;
+
+ for (x = s, i = 1; i < m; x++, i++)
{
- int c = 0;
- int c1 = 0;
- int c2 = 0;
- int c3 = 0;
-
- /*
- * The "cost" value is 0 if the character at the current col
- * position in the source string, matches the character at the
- * current row position in the target string; cost is 1 otherwise.
- */
- c = (*str_s != *str_t);
-
- /*
- * c1 is upper right cell plus 1
- */
- c1 = u_cells[i] + 1;
+ int ins;
+ int del;
+ int sub;
+
+ /* Calculate costs for probable operations. */
+ ins = prev[i] + ins_c; /* Insertion */
+ del = curr[i-1] + del_c; /* Deletion */
+ sub = prev[i-1] + ((*x == *y) ? 0 : sub_c); /* Substitution */
+
+ /* Take the one with minimum cost. */
+ curr[i] = Min(ins, del);
+ curr[i] = Min(curr[i], sub);
+ }
- /*
- * c2 is lower left cell plus 1
- */
- c2 = l_cells[i - 1] + 1;
+ /* Swap current row with previous row. */
+ temp = curr;
+ curr = prev;
+ prev = temp;
+ }
- /*
- * c3 is cell diagonally above to the left plus "cost"
- */
- c3 = u_cells[i - 1] + c;
+ /*
+ * Because the final value was swapped from the previous row to
+ * the current row, that's where we'll find it.
+ */
+ return prev[m-1];
+}
- /*
- * The lower right cell is set to the minimum of c1, c2, c3
- */
- l_cells[i] = (c1 < c2 ? c1 : c2) < c3 ? (c1 < c2 ? c1 : c2) : c3;
- /*
- * Increment the pointer to str_s
- */
- str_s++;
- }
+PG_FUNCTION_INFO_V1(levenshtein_with_costs);
+Datum
+levenshtein_with_costs(PG_FUNCTION_ARGS)
+{
+ char *src = TextDatumGetCString(PG_GETARG_DATUM(0));
+ char *dst = TextDatumGetCString(PG_GETARG_DATUM(1));
+ int ins_c = PG_GETARG_INT32(2);
+ int del_c = PG_GETARG_INT32(3);
+ int sub_c = PG_GETARG_INT32(4);
- /*
- * Lower row now becomes the upper row, and the upper row gets reused
- * as the new lower row.
- */
- tmp = u_cells;
- u_cells = l_cells;
- l_cells = tmp;
+ PG_RETURN_INT32(levenshtein_internal(src, dst, ins_c, del_c, sub_c));
+}
- /*
- * Increment the pointer to str_t
- */
- str_t++;
- /*
- * Rewind the pointer to str_s
- */
- str_s = str_s0;
- }
+PG_FUNCTION_INFO_V1(levenshtein);
+Datum
+levenshtein(PG_FUNCTION_ARGS)
+{
+ char *src = TextDatumGetCString(PG_GETARG_DATUM(0));
+ char *dst = TextDatumGetCString(PG_GETARG_DATUM(1));
- /*
- * Because the final value (at position row, col) was swapped from the
- * lower row to the upper row, that's where we'll find it.
- */
- PG_RETURN_INT32(u_cells[cols - 1]);
+ PG_RETURN_INT32(levenshtein_internal(src, dst, 1, 1, 1));
}
+
/*
* Calculates the metaphone of an input string.
* Returns number of characters requested
@@ -249,9 +349,8 @@ metaphone(PG_FUNCTION_ARGS)
/*
* Original code by Michael G Schwern starts here.
* Code slightly modified for use as PostgreSQL
- * function (palloc, etc). Original includes
- * are rolled into fuzzystrmatch.h
- *------------------------------------------------------------------*/
+ * function (palloc, etc).
+ */
/* I suppose I could have been using a character pointer instead of
* accessing the array directly... */
@@ -273,7 +372,7 @@ metaphone(PG_FUNCTION_ARGS)
/* Allows us to safely look ahead an arbitrary # of letters */
/* I probably could have just used strlen... */
-char
+static char
Lookahead(char *word, int how_far)
{
char letter_ahead = '\0'; /* null by default */
@@ -299,14 +398,10 @@ Lookahead(char *word, int how_far)
#define Isbreak(c) (!isalpha((unsigned char) (c)))
-int
-_metaphone(
- /* IN */
- char *word,
+static int
+_metaphone(char *word, /* IN */
int max_phonemes,
- /* OUT */
- char **phoned_word
-)
+ char **phoned_word) /* OUT */
{
int w_idx = 0; /* point in the phonization we're at. */
int p_idx = 0; /* end of the phoned phrase */
diff --git a/contrib/fuzzystrmatch/fuzzystrmatch.h b/contrib/fuzzystrmatch/fuzzystrmatch.h
deleted file mode 100644
index 22670ba9483..00000000000
--- a/contrib/fuzzystrmatch/fuzzystrmatch.h
+++ /dev/null
@@ -1,171 +0,0 @@
-/*
- * fuzzystrmatch.h
- *
- * Functions for "fuzzy" comparison of strings
- *
- * Joe Conway <mail@joeconway.com>
- *
- * $PostgreSQL: pgsql/contrib/fuzzystrmatch/fuzzystrmatch.h,v 1.17 2008/03/25 22:42:41 tgl Exp $
- * Copyright (c) 2001-2008, PostgreSQL Global Development Group
- * ALL RIGHTS RESERVED;
- *
- * levenshtein()
- * -------------
- * Written based on a description of the algorithm by Michael Gilleland
- * found at http://www.merriampark.com/ld.htm
- * Also looked at levenshtein.c in the PHP 4.0.6 distribution for
- * inspiration.
- *
- * metaphone()
- * -----------
- * Modified for PostgreSQL by Joe Conway.
- * Based on CPAN's "Text-Metaphone-1.96" by Michael G Schwern <schwern@pobox.com>
- * Code slightly modified for use as PostgreSQL function (palloc, elog, etc).
- * Metaphone was originally created by Lawrence Philips and presented in article
- * in "Computer Language" December 1990 issue.
- *
- * Permission to use, copy, modify, and distribute this software and its
- * documentation for any purpose, without fee, and without a written agreement
- * is hereby granted, provided that the above copyright notice and this
- * paragraph and the following two paragraphs appear in all copies.
- *
- * IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY FOR
- * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
- * LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
- * DOCUMENTATION, EVEN IF THE AUTHOR OR DISTRIBUTORS HAVE BEEN ADVISED OF THE
- * POSSIBILITY OF SUCH DAMAGE.
- *
- * THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES,
- * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
- * AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
- * ON AN "AS IS" BASIS, AND THE AUTHOR AND DISTRIBUTORS HAS NO OBLIGATIONS TO
- * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
- *
- */
-
-#ifndef FUZZYSTRMATCH_H
-#define FUZZYSTRMATCH_H
-
-#include "postgres.h"
-
-#include <ctype.h>
-
-#include "fmgr.h"
-#include "utils/builtins.h"
-
-
-
-/*
- * External declarations
- */
-extern Datum levenshtein(PG_FUNCTION_ARGS);
-extern Datum metaphone(PG_FUNCTION_ARGS);
-extern Datum soundex(PG_FUNCTION_ARGS);
-extern Datum difference(PG_FUNCTION_ARGS);
-
-/*
- * Soundex
- */
-static void _soundex(const char *instr, char *outstr);
-
-#define SOUNDEX_LEN 4
-
-/* ABCDEFGHIJKLMNOPQRSTUVWXYZ */
-static const char *soundex_table = "01230120022455012623010202";
-
-#define soundex_code(letter) soundex_table[toupper((unsigned char) (letter)) - 'A']
-
-
-/*
- * Levenshtein
- */
-#define MAX_LEVENSHTEIN_STRLEN 255
-
-
-/*
- * Metaphone
- */
-#define MAX_METAPHONE_STRLEN 255
-
-/*
- * Original code by Michael G Schwern starts here.
- * Code slightly modified for use as PostgreSQL
- * function (combined *.h into here).
- *------------------------------------------------------------------*/
-
-/**************************************************************************
- metaphone -- Breaks english phrases down into their phonemes.
-
- Input
- word -- An english word to be phonized
- max_phonemes -- How many phonemes to calculate. If 0, then it
- will phonize the entire phrase.
- phoned_word -- The final phonized word. (We'll allocate the
- memory.)
- Output
- error -- A simple error flag, returns TRUE or FALSE
-
- NOTES: ALL non-alpha characters are ignored, this includes whitespace,
- although non-alpha characters will break up phonemes.
-****************************************************************************/
-
-
-/**************************************************************************
- my constants -- constants I like
-
- Probably redundant.
-
-***************************************************************************/
-
-#define META_ERROR FALSE
-#define META_SUCCESS TRUE
-#define META_FAILURE FALSE
-
-
-/* I add modifications to the traditional metaphone algorithm that you
- might find in books. Define this if you want metaphone to behave
- traditionally */
-#undef USE_TRADITIONAL_METAPHONE
-
-/* Special encodings */
-#define SH 'X'
-#define TH '0'
-
-char Lookahead(char *word, int how_far);
-int
-_metaphone(
- /* IN */
- char *word,
- int max_phonemes,
- /* OUT */
- char **phoned_word
-);
-
-/* Metachar.h ... little bits about characters for metaphone */
-
-
-/*-- Character encoding array & accessing macros --*/
-/* Stolen directly out of the book... */
-char _codes[26] = {
- 1, 16, 4, 16, 9, 2, 4, 16, 9, 2, 0, 2, 2, 2, 1, 4, 0, 2, 4, 4, 1, 0, 0, 0, 8, 0
-/* a b c d e f g h i j k l m n o p q r s t u v w x y z */
-};
-
-
-#define ENCODE(c) (isalpha((unsigned char) (c)) ? _codes[((toupper((unsigned char) (c))) - 'A')] : 0)
-
-#define isvowel(c) (ENCODE(c) & 1) /* AEIOU */
-
-/* These letters are passed through unchanged */
-#define NOCHANGE(c) (ENCODE(c) & 2) /* FJMNR */
-
-/* These form dipthongs when preceding H */
-#define AFFECTH(c) (ENCODE(c) & 4) /* CGPST */
-
-/* These make C and G soft */
-#define MAKESOFT(c) (ENCODE(c) & 8) /* EIY */
-
-/* These prevent GH from becoming F */
-#define NOGHTOF(c) (ENCODE(c) & 16) /* BDH */
-
-#endif /* FUZZYSTRMATCH_H */
diff --git a/contrib/fuzzystrmatch/fuzzystrmatch.sql.in b/contrib/fuzzystrmatch/fuzzystrmatch.sql.in
index c4b678f90fa..cab78997fa7 100644
--- a/contrib/fuzzystrmatch/fuzzystrmatch.sql.in
+++ b/contrib/fuzzystrmatch/fuzzystrmatch.sql.in
@@ -1,4 +1,4 @@
-/* $PostgreSQL: pgsql/contrib/fuzzystrmatch/fuzzystrmatch.sql.in,v 1.9 2007/11/13 04:24:28 momjian Exp $ */
+/* $PostgreSQL: pgsql/contrib/fuzzystrmatch/fuzzystrmatch.sql.in,v 1.10 2008/04/03 21:13:07 tgl Exp $ */
-- Adjust this setting to control where the objects get created.
SET search_path = public;
@@ -7,6 +7,10 @@ CREATE OR REPLACE FUNCTION levenshtein (text,text) RETURNS int
AS 'MODULE_PATHNAME','levenshtein'
LANGUAGE C IMMUTABLE STRICT;
+CREATE OR REPLACE FUNCTION levenshtein (text,text,int,int,int) RETURNS int
+AS 'MODULE_PATHNAME','levenshtein_with_costs'
+LANGUAGE C IMMUTABLE STRICT;
+
CREATE OR REPLACE FUNCTION metaphone (text,int) RETURNS text
AS 'MODULE_PATHNAME','metaphone'
LANGUAGE C IMMUTABLE STRICT;
diff --git a/contrib/fuzzystrmatch/uninstall_fuzzystrmatch.sql b/contrib/fuzzystrmatch/uninstall_fuzzystrmatch.sql
index 212e7b72830..bcf05da1322 100644
--- a/contrib/fuzzystrmatch/uninstall_fuzzystrmatch.sql
+++ b/contrib/fuzzystrmatch/uninstall_fuzzystrmatch.sql
@@ -1,4 +1,4 @@
-/* $PostgreSQL: pgsql/contrib/fuzzystrmatch/uninstall_fuzzystrmatch.sql,v 1.3 2007/11/13 04:24:28 momjian Exp $ */
+/* $PostgreSQL: pgsql/contrib/fuzzystrmatch/uninstall_fuzzystrmatch.sql,v 1.4 2008/04/03 21:13:07 tgl Exp $ */
-- Adjust this setting to control where the objects get dropped.
SET search_path = public;
@@ -15,4 +15,6 @@ DROP FUNCTION soundex(text);
DROP FUNCTION metaphone (text,int);
+DROP FUNCTION levenshtein (text,text,int,int,int);
+
DROP FUNCTION levenshtein (text,text);
diff --git a/doc/src/sgml/fuzzystrmatch.sgml b/doc/src/sgml/fuzzystrmatch.sgml
index 1eb1ad61843..62ab943ff7d 100644
--- a/doc/src/sgml/fuzzystrmatch.sgml
+++ b/doc/src/sgml/fuzzystrmatch.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/fuzzystrmatch.sgml,v 1.3 2007/12/06 04:12:10 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/fuzzystrmatch.sgml,v 1.4 2008/04/03 21:13:07 tgl Exp $ -->
<sect1 id="fuzzystrmatch">
<title>fuzzystrmatch</title>
@@ -74,16 +74,20 @@ SELECT * FROM s WHERE difference(s.nm, 'john') > 2;
</para>
<programlisting>
+ levenshtein(text source, text target, int ins_cost, int del_cost, int sub_cost) returns int
levenshtein(text source, text target) returns int
</programlisting>
<para>
Both <literal>source</literal> and <literal>target</literal> can be any
- non-null string, with a maximum of 255 characters.
+ 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.
</para>
<para>
- Example:
+ Examples:
</para>
<programlisting>
@@ -92,6 +96,12 @@ test=# SELECT levenshtein('GUMBO', 'GAMBOL');
-------------
2
(1 row)
+
+test=# SELECT levenshtein('GUMBO', 'GAMBOL', 2,1,1);
+ levenshtein
+-------------
+ 3
+(1 row)
</programlisting>
</sect2>
--
GitLab