title: Check property value uniqueness in cypher
body: <p>Without enforcing a constraint, I would like to <strong>check</strong> for a property value uniqueness. I thought this would work:</p>
  <pre><code>MATCH (n:SomeLabel)
  WHERE n.uuid IS NOT null
  RETURN count(n.uuid) = count(DISTINCT n.uuids) AS is_unique
  </code></pre>
  <p>This returned <code>false</code> even though I know it's true. I then tried:</p>
  <pre><code>MATCH (n:SomeLabel)
  WHERE n.uuid IS NOT null
  RETURN count(n.uuid), count(DISTINCT n.uuids)
  </code></pre>
  <p>and discovered the second count is 0. How come?!<br>
  What's wrong with this query and would this be a good way to check uniqueness?</p>