title: Group by numbers that are in sequence
body: <p>I have some data like this:</p>
  
  <pre><code>row    id
  1      1
  2      36
  3      37
  4      38
  5      50
  6      51
  </code></pre>
  
  <p>I would like to query it to look like this:</p>
  
  <pre><code> row    id    group
   1      1     1
   2      36    2
   3      37    2
   4      38    2
   5      50    3
   6      51    3
  </code></pre>
  
  <p>... so that I can GROUP BY where the numbers are consecutively sequential.</p>
  
  <p>Also, looping/cursoring is out of the question since I'm working with a pretty large set of data, thanks.</p>