title: Calculate percentage of group using GROUP BY
body: <p>I am doing a GROUP BY and COUNT(*) on a dataset, and I would like to calculate the percentage of each group over the total.</p>
  
  <p>For example, in this query, I would like to know how much the count(<em>) for each state represents over the total ( select count(</em>) from publicdata:samples.natality ):</p>
  
  <pre><code>SELECT state, count(*)
  FROM [publicdata:samples.natality]
  GROUP by state
  </code></pre>
  
  <p>There are several ways to do it in SQL, but I haven't found a way to do it in Bigquery, does anyone know?</p>
  
  <p>Thanks!</p>