What does the Postgres  operator do? I was reading through the Postgres documentation on materialized views and in one example they use the following:

SELECT word FROM words ORDER BY word &lt;-&gt; 'caterpiler' LIMIT 10;


I tried to run a similar query on my own database, but I get an error.

[42883] ERROR: operator does not exist: character varying &lt;-&gt; unknown


I (probably) don't need to use the operator, but I'm just curious what it does.

Notes:


I am running the same version as the docs (9.3)
I did try Googling the question, but Google just ignores the &lt;-&gt; even if you wrap it in quotes.
It's supposed to be the "distance" operator from the additional module pg_trgm.

The manual:


  text &lt;-&gt; text   real  Returns the "distance" between the arguments, that is one minus the similarity() value.


The module has to be installed (once per database) with:

CREATE EXTENSION pg_trgm;


More details:


How is LIKE implemented?


Theoretically, any user with the necessary privileges could create an operator with that operator name using CREATE OPERATOR - but not in the example you link to.