title: Is there any purpose to creating a clustered index on a column that only contains null?
body: <p>We are running a Sitecore CMS system and store the data in a MS SQL database.  On some of the tables, I see a column named DAC_Index.  The value in this field is all null.  And then there is a Clustered Index created on this field.</p>
  
  <ol>
  <li>What purpose is there to cluster index a field of all Nulls?</li>
  <li>Could this be to prevent anyone from creating a clustered index on another field?</li>
  <li>Is there any negative performance implications that having this field causes?</li>
  <li>Is it possible some 3rd party component or standard .NET component leverages a DAC_Index column for something, so maybe it's just required to be there?  But then, still I wonder why there needs to be a clustered index.</li>
  </ol>
  
  <p>It is possible that the data in that field changes occasionally (maybe during something transactional happening to a set of rows).  I just know that when I've queried the data, it always come back as all Null.</p>
  
  <p>Any insight on the purpose of this and/or what performance implications are of having this?</p>