title: How do I return my records grouped by NULL and NOT NULL?
body: <p>I have a table that has a <code>processed_timestamp</code> column -- if a record has been processed then that field contains the datetime it was processed, otherwise it is null.</p>
  
  <p>I want to write a query that returns two rows:</p>
  
  <pre><code>NULL        xx -- count of records with null timestamps
  NOT NULL    yy -- count of records with non-null timestamps
  </code></pre>
  
  <p>Is that possible?</p>
  
  <p><strong>Update:</strong> The table is quite large, so efficiency is important. I could just run two queries to calculate each total separately, but I want to avoid hitting the table twice if I can avoid it.</p>