Fuzzy Logic SQL select framework
bayareaguy: This was a hot topic in databases 20 years ago and there have been
various academic projects which implemented user defined types and 
operators to do this for systems like PostgreSQL.Most of them haven't produced any useful code but a quick search 
turned up this more promising site:
http://calypso.cs.put.poznan.pl/~sqlf_j/en/index.php  SQLf_j is a query system, that enables fuzzy queries to relational
  database managements systems (currently: MySQL and PostgreSQL). The
  queries are written in SQLf which is an extension to SQL. SQLf_j
  works as a translator, that translates fuzzy queries to standard,
  SQL queries, and executes them with RDBMS.

There also seems to be some interesting stuff here:
http://www.ecst.csuchico.edu/~juliano/Fuzzy