title: How to calculate percentage of total in Athena (Presto)?
body: <p>Given a table with columns such as:</p>
  <pre><code>Date, Type
  </code></pre>
  <p>I'm running the following SQL:</p>
  <pre><code>SELECT Type, count(*) as CountPerType
  FROM myTable
  WHERE Date between 20200101 and 20200131
  GROUP BY count(*)
  </code></pre>
  <p>I want to have an extra column <code>Percentage</code> which will have <code>100.0 * CountPerType / SUM(CountPerType)</code>. What's the most efficient way to do it in PrestoDB (which powers Amazon Athena)?</p>