title: Custom Group By and place some records in one group
body: <p>please consider data:</p>
  
  <pre><code> Id          Group            Value
   -----------------------------------
   1            1                10
   2            1                12
   3            1                10
   4            2                90
   5            2                10
   6            3                30
   7            4                12
   8            4                11
   9            5                10
   10           5                11
  </code></pre>
  
  <p>I want to do <code>Group By</code> on this data as <code>1,2,3</code> place in one group and <code>4,5</code> place in another group. How I can do this with <code>SQL Server</code>?</p>
  
  <p>thanks</p>
  
  <hr>
  
  <p><strong>Edit 1)</strong></p>
  
  <p>I want this result:</p>
  
  <pre><code>Groups                              Count
  -----------------------------------------
  Group for 1,2,3                       6
  Group for 4,5                         4
  </code></pre>