title: Oracle SQL division
body: <p>I have </p>
  
  <pre><code>SELECT 
  COUNT(*) AS a,
  SUM(CASE WHEN r.hn IS NOT NULL THEN 1 ELSE 0 END) AS b,
  SUM(CASE WHEN r.hn IS NULL THEN 1 ELSE 0 END) AS c,
  ( ____ / ____ ) AS d
  FROM
  x
  LEFT JOIN (SELECT DISTINCT xn FROM yn) r ON x.xn = y.xn;
  </code></pre>
  
  <p>I need the blanks on line 4 to be the values set to 'a' and 'c', I'm not sure what the correct syntax is though.</p>