title: ERROR: Operand data type nvarchar is invalid for sum operator
body: <p>The error occurs on Line 5 where I try to <code>SUM(genre) AS "Total"</code>.</p>
  
  <p>I've tried <code>convert</code>ing <code>genre</code> to <code>int</code> or <code>cast</code>ing as <code>int</code>, both led to an Action error.</p>
  
  <pre><code>USE IMDB
  SELECT
      CAST(genre AS CHAR(20)) AS "Genre",
      COUNT (genre) AS "Count",
      SUM (genre) AS "Total"
      /*STR(100*COUNT (genre) / SUM(SUM( genre)) OVER (), 6, 2) + '%' AS "Percent"*/
  FROM title_genre
  GROUP BY genre
  ORDER BY "Count" DESC;
  </code></pre>