title: Group by without an aggregate function
body: <p>I've seen a <code>pandasql</code> query like this:</p>
  
  <pre><code>df = pd.DataFrame({'A': [1, 2, 2], 'B': [3, 4, 5]})
  sqldf('select * from df group by A', locals())
  </code></pre>
  
  <p>This gives:</p>
  
  <pre><code>   A  B
  0  1  3
  1  2  6
  </code></pre>
  
  <p>I find it really weird to have a group by without an aggregate function, but can anyone tell me which function is used on the aggregated columns to reduce multiple values into one?</p>