title: gaps in employment history
body: <p>I have a simple employment history database, I store the entry id, user id, their job, start and end date.  There may be some overlapping entries.  I need to establish that in a given period there are no breaks of a given timeframe.</p>
  
  <p>So user_id 1 have a work history like so</p>
  
  <pre><code>Marketing - 01/01/2013 to 19/05/2013
  Sales - 01/01/2011 to 01/05/2012
  Admin - 01/01/2010 to 31/12/2010
  </code></pre>
  
  <p>I actually store the dates as unix timestamp.  In a three year history user_id 1 has a break of over 6 months between their sales job and their marketing job.  How can I flag this to them so they can provide an entry for this period.</p>