The fuzzystrmatch module (
http://www.postgresql.org/docs/9.2/static/fuzzystrmatch.html) is currently, as of 9.2.1, documented with the caution
"At present, the soundex, metaphone, dmetaphone, and dmetaphone_alt functions do not work well with multibyte encodings (such as UTF-8)".
While the venerable algorithms contained in the module seem to generally work for Latin strings from European languages which all have accented/diacritic characters such as äöüñáéíóúàèìòù, for languages with non-Latin characters such as Kyrillic, Hebrew, Arabic, Chinese, these venerable algorithms return NULL (empty) or plain weirdness.
Some examples:
dmetaphone ('Новости') = 'NN'
soundex ('Новости') = NULL
dmetaphone ('לפחות') = NULL
soundex ('לפחות') = NULL
soundex ('相关搜索') = NULL
dmetaphone ('相关搜索') = NULL
metaphone() crashes with SQL state: 42883 for all these strings (it tells me I should cast the 'unknown' input).
The string 'äöüñáéíóúàèìòù' causes metaphone(), dmetaphone(), dmetaphone_alt, soundex() to fail.
Only levenshtein() appears to function correctly with all above inputs, even when I let it compare Hebrew against Chinese strings.
Summarizing my experience:
* for english (ASCII equivalent), the module works,
* for the rest of the Latin charsets (equivalent to ISO 8859-x) the module works unreliably,
* for non-latin chars (UTF8 with 2-4 bytes per char) the module does not work
Note: My DB and the OS are set up for UTF-8.
This would appear to be less a problem of Postgresql and the fuzzystrmach module itself but because there
appear to exist no replacement algorithms adequate for a multilingual world - at least that is my impression
Given all this I have no idea of this is a bug at all or the state-of-the-art around this topic is inadequate.
Questions (to the developers):
- Is there anything in work or planned for the fuzzystrmatch module?
- Does anybody know about adequate replacements or upgrades of the soundex, metaphone etc. algorithms from academia?
