title: SQLAlchemy: Further filter query with label
body: <p>I have a query that yields an id, followed by a count.  I want to get only those rows which have a count of N.  I tried the code below but I get 'error: column "cert_count" does not exist'.  I guess I'm using the label wrong?</p>
  
  <pre><code>cust_cert_counts = db.session.query(
      CustomerCertAssociation.customer_id,
      func.count(CustomerCertAssociation.certification_id).label('cert_count')).filter(
      CustomerCertAssociation.certification_id.in_(cert_ids)).group_by(
      CustomerCertAssociation.customer_id)
  cust_cert_counts.filter('cert_count=2').all()
  </code></pre>