title: H2: SELECT DISTINCT slow despite low selectivity
body: <p>I am using H2 and have a simple query that looks like this:</p>
  
  <pre><code>SELECT DISTINCT col
  FROM PUBLIC.TABLE;
  </code></pre>
  
  <p>H2 uses a full table scan, even though the selectivity is low, and there is a non-unique index on col. </p>
  
  <p>I checked this and ran:</p>
  
  <pre><code>SELECT SELECTIVITY(CLUSTERNODE ) FROM PUBLIC.TRANSFORMATION;
  </code></pre>
  
  <p>Which returned '1'.</p>
  
  <p>Any ideas?</p>