title: JPA count distinct multiple expressions
body: <p>CriteriaBuilder.countDistinct(Expression e)</p>
  
  <p>It takes one expression only. How to count distinct multiple expressions? For example,</p>
  
  <pre><code>Country              Language
  -------------------------------
  </code></pre>
  
  <p>In JPA CriteriaQuery, how to count different pairs of (country, language)?</p>
  
  <p>Thanks,</p>