title: Postgres ts_rank_cd: No function matches the given name and argument type
body: <p>I am using Postgres 9.1 and trying to get fulltext ranking working.</p>
  
  <p>I am following</p>
  
  <p><a href="http://www.postgresql.org/docs/9.1/static/textsearch-controls.html#TEXTSEARCH-RANKING" rel="nofollow noreferrer">http://www.postgresql.org/docs/9.1/static/textsearch-controls.html#TEXTSEARCH-RANKING</a></p>
  
  <pre><code>nutrition=&gt; SELECT title, ts_rank_cd(title, query) AS rank FROM food.usda, to_tsquery('egg') query WHERE query @@ title order by rank desc;
  ERROR:  function ts_rank_cd(character varying, tsquery) does not exist
  LINE 1: SELECT title, ts_rank_cd(title, query) AS rank FROM food.usd...
                    ^
  HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
  </code></pre>
  
  <p>There is a related posting</p>
  
  <p><a href="https://stackoverflow.com/questions/3501831/function-ts-rank-cdtext-tsquery-does-not-exist">function ts_rank_cd(text, tsquery) does not exist</a></p>
  
  <p>but why does my query not work? Is this a documentation error? I am just following the basic example from the 9.1 docs.</p>