title: get number of working days from date range in SQL for sqlite without extension functions
body: <p>I have a table that contains the columns <em>start</em> and <em>end</em>, which contain the start and end date of a date range. I want to select the number of working days (number of days excluding saturday and sunday) using pure sqlite3 functionality from each time range. Is there any way to do this?</p>
  
  <p>I checked the several answers for this problem, but many seem to use functions like <code>DATEDIFF</code> which aren't available in sqlite.</p>
  
  <p>Example: Start date '2015-09-19' and end date '2015-09-22' should result in two working days.</p>