Similarity function in Postgres with pg_trgm

With postgresql 9.1:

after installing (on ubuntu) sudo apt-get install postgresql-contrib as tomaszbak answered.

you just have to execute the sql command:

CREATE EXTENSION pg_trgm;

On ubuntu you need to run

sudo apt-get install postgresql-contrib

to get /usr/share/postgresql/8.4/contrib/pg_trgm.sql

You have to install pg_trgm. In debian, source this sql: /usr/share/postgresql/8.4/contrib/pg_trgm.sql. From the command line:

psql -f /usr/share/postgresql/8.4/contrib/pg_trgm.sql

Or inside a psql shell:

\i /usr/share/postgresql/8.4/contrib/pg_trgm.sql

The script defaults to installing in the public schema, edit the search path at the top if you want to install it somewhere else (so that uninstalling/upgrading can be done simply by dropping the schema).