title: sqlalchemy exists for query
body: <p>How do I check whether data in a query exists?</p>
  
  <p>For example:</p>
  
  <pre><code>users_query = User.query.filter_by(email='x@x.com')
  </code></pre>
  
  <p>How I can check whether users with that email exist?</p>
  
  <p>I can check this with </p>
  
  <pre><code>users_query.count()
  </code></pre>
  
  <p>but how to check it with <strong>exists</strong>?</p>