title: Find records that qualify as pairs
body: <p>I have a sql database which looks like this:</p>
  
  <p><img src="https://i.stack.imgur.com/etgUI.png" alt="enter image description here"></p>
  
  <p>I want to get all <code>EAN</code>s (european article number, it's like a sku) where <code>stock_level</code> is <code>Null</code>, and which have a duplicate" (where duplicate means same <code>style</code>, <code>color</code> and <code>size</code>)</p>
  
  <p>So the red cells represent this kind of "duplicate" pair, so <code>EAN</code> <code>400006</code> would be what I want to output and later delete.</p>
  
  <p>Knowing how I can group and count, I still can't figure out a way to isolate the <code>EAN</code>s.</p>