title: How to find not-crossing time sets using SQL?
body: <p>I have N records in table T. Each has time interval - startTime, endTime in unix timestamp format. I want to generate a list of time intervals (start+end times) from lowest startTime to Now, where no record had time interval at that time. How to do such thing with MySQL?</p>
  
  <p>Having data like <a href="http://sqlfiddle.com/#!2/13fddf/9" rel="nofollow">this</a>
  we would like to get values</p>
  
  <pre><code>(3, 4)
  (9, 10)
  (13, NOW())
  </code></pre>