title: how to find Group By in grails using createCriteria
body: <p>I have a domain</p>
  
  <pre><code>class File{
    String fileName
    String account
    int fileSize
  }
  </code></pre>
  
  <p>i have to find filesize group by account like this</p>
  
  <pre><code>account1 = filesize1+filesize2.....
  account2= fs1+fs2+.....
  </code></pre>
  
  <p>so how can i create a GORM query using criteria
  thank </p>