title: Is there a more concise way to check if PGResult is empty?
body: <p>I'm using the <code>pg</code> gem to talk to PostgreSQL from Ruby. Is there a
  better way to check if there are no results than using <code>res.ntuples == 0</code>?</p>
  
  <pre><code>conn = PGconn.connect config
  
  cmd = "select * from labels inner join labels_mail using(label_id) " + 
    "where labels_mail.mail_id = $1 and labels.name = $2"
  
  res = conn.exec(cmd, [mail_id, mailbox])
  
  if res.ntuples == 0  #  &lt;=== is there a better way to check this?
    cmd = "insert into labels_mail (mail_id, label_id) values ($1, $2)"
    conn.exec(cmd, [mail_id, label_id(mailbox)])
  end
  </code></pre>