title: PostgreSQL DBLink: No function matches the given name and argument types
body: <p>I was playing around with DBLINK and I wanted to try it. So I run this simple query</p>
  
  <pre><code>CREATE EXTENSION dblink;
  
  SELECT *  
  FROM dblink(('dbname=genesis_admin')::text,
        ('SELECT * FROM user_account')::text);
  </code></pre>
  
  <p>then to my surprise</p>
  
  <pre><code>[WARNING  ] CREATE EXTENSION dblink
              ERROR:  extension "dblink" already exists
  [WARNING  ] SELECT *  FROM dblink(('dbname=genesis_admin')::text, ('SELECT * FROM user_account')::text)
              ERROR:  function dblink(text, text) does not exist
              LINE 1: SELECT *  FROM dblink(('dbname=genesis_admin')::text, ('SELE...
                                     ^
              HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
  </code></pre>
  
  <p>How can it not be existing if it already exists? </p>