title: For xml path returns null instead of nothing
body: <p>I thought that following query suppose to return nothing, but, instead, it returns one record with a column containing <code>null</code>:</p>
  
  <pre><code>select *
  from ( select 1 as "data"
         where 0 = 1
         for xml path('row') ) as fxpr(xmlcol)
  </code></pre>
  
  <p>If you run just the subquery - nothing is returned, but when this subquery has an outer query, performing a <code>select</code> on it, <code>null</code> is returned.</p>
  
  <p>Why is that happening?</p>