For those people coming from Oracle, SQL Server and MySQL or other databases that have soundex functionality,
you may be puzzled, or even frustrated when you try to do
something like WHERE soundex('Wushington') = soundex('Washington') in PostgreSQL and get a function does not exist error.
Well it does so happen that there is a soundex function in PostgreSQL, and yes it is
also called soundex, but is offered as a contrib module and not installed by default. It also has other fuzzy string matching functions in addition to soundex.
One of my favorites, the levenshenstein distance function is included as well. In this article
we'll be covering the contrib module packaged as fuzzystrmatch.sql. Details of the module can be found in FuzzyStrMatch.
The contrib module has been around for sometime, but has changed slightly from PostgreSQL version to PostgreSQL version. We are covering the 8.4 version in this article.
For those unfamiliar with soundex, its a basic approach developed by the US Census in the 1930s as a way of sorting
names by pronounciation. Read Census and Soundex for more gory history details.
Given that it is an approach designed primarily for the English alphabet, it sort of makes sense why its not built-in to PostgreSQL,
which has more of a diverse international concern. For example if you used it to compare two words in Japanese or Chinese,
don't think it would fair too well in any of the database platforms that support this function.
The original soundex algorithm has been improved over the years. Though its still the most common used today, newer variants
exist called MetaPhone developed in the 1990s and Double Metaphone (DMetaPhone) developed in 2000 that support additional
consonants in other languages such as Slavic, Celtic, Italian, Spanish etc.
These two variants are also included in the fuzzystrmatch contrib library. The soundex function still seems to be
the most popularly used at least for U.S. This is perhaps because most of the other databases (Oracle, SQL Server, MySQL) have soundex built-in but not the metaphone variants.
So in a sense soundex is a more portable function. The other reason is that metaphone and dmetaphone take up a bit more space and
are also more processor intensive to compute than soundex. We'll demonstrate some differences between them in this article.
To enable soundex and the other fuzzy string matching functions included, just run the
share/contrib/fuzzystrmatch.sql located in your PostgreSQL install folder. This library is an important piece of arsenal for geocoding and genealogy tracking particularly
the U.S. streets and surnames data sets. I come from a long line of Minors, Miners, Burnettes and Burnets.