title: what does datediff in tsql return
body: <p>I have the following sql which returns the date of last monday.</p>
  
  <pre><code>SELECT  DATEADD(wk, DATEDIFF(wk, 6, GETDATE()), 0) //2017-05-15 00:00:00.000
  </code></pre>
  
  <p>However in trying to understand how this has been worked out, I'm confused 
   as to what the 6124 returned by the following represents</p>
  
  <pre><code> SELECT  DATEDIFF(wk, 6, GETDATE())
  </code></pre>
  
  <p>It's only last week why is it such a high number?</p>
  
  <p>Also how can the offset be a fixed number and still be able to work out the date of the previous monday </p>