title: How is it possible for count distinct to show duplicates, but group by does not?
body: <p>I want to query for duplicates in my data.  </p>
  
  <p>So, the first thing I do is I do a count distinct:</p>
  
  <pre><code>select count(distinct colA, colB ....) from Table
  </code></pre>
  
  <p>and a count:</p>
  
  <pre><code>select count(*) from Table
  </code></pre>
  
  <p>And I see that the count distinct is lower than the count(*).<br>
  So, now I want to actually see the duplicates, so I do this:</p>
  
  <pre><code>select colA, colB, .... count(*) from Table 
  group by colA, colB ... having count(*) &gt; 1;
  </code></pre>
  
  <p>Now, for some reason, this does not return any records at all.  The table is too big for me to show results here, and the columns too many.  </p>
  
  <p>How is it possible for both of these to be true?  the counts are different, but no rows show up when I group them and filter for <code>count(*) &gt;1</code>?</p>
  
  <p>Thanks.</p>