title: Confusion over the second argument of the DATEDIFF function
body: <p>I've referred to <a href="http://msdn.microsoft.com/en-us/library/aa258269%28v=sql.80%29.aspx" rel="noreferrer">this on MSDN</a> but I'm still unsure what the second argument in the DATEDIFF function is doing in the following two examples:</p>
  
  <p><code>SELECT DATEDIFF(yy,0,getdate())</code>  --run on 14 Aug this returns 112</p>
  
  <p><code>SELECT DATEDIFF(yy,1000,getdate())</code>  --I chose 1000 arbitrarily and run on 14 Aug this returns 110</p>
  
  <p>Usually I'll use <code>DATEDIFF</code> to find the number of days, or number of years between two months and the second argument is then a date.</p>
  
  <p>Reason I'd like to understand the above is to ultimately understand the following:</p>
  
  <p><code>SELECT DATEADD(yy, DATEDIFF(yy,0,GETDATE()), 0)</code></p>