title: Total of group by divided by total of group by after where statement
body: <p>I get the total number after grouping by and the total of the filled rows after grouping by.</p>
  <pre><code>SELECT X, COUNT(*) as total
  FROM table 
  WHERE Y IS NULL 
  GROUP BY X
  </code></pre>
  <p>This for example results in row 1 has 1000 values</p>
  <pre><code>SELECT X, COUNT(*) as total
  FROM table
  GROUP BY X
  </code></pre>
  <p>this for examples results in row 1 has 500 values.</p>
  <p>Now what I want to get is the proportion. Meaning I want to get the total of my group by statement divided by the total of my group by statement with the WHERE filter. Is this possible?</p>