title: SQL query calculate percent true from 10 boolean columns
body: <p>I have a table called "Grades" with 10 boolean columns called PassA, PassB, PassC, PassD, etc.
  I am trying to make a query that will give me the percent of "true" in each column?</p>
  
  <pre><code>ID   PassA  PassB   PassC
  1      x      x       
  2             x       x
  3      x
  4             x
  </code></pre>
  
  <p>Expected query result (or equivalent):</p>
  
  <pre><code>PassA  PassB   PassC
  50%    75%     25%
  </code></pre>
  
  <p>It is an Access SQL statement.</p>
  
  <p>I seem to be able to do it with one column (see below) but wan't to do it will all the columns in 1 query. All ideas are very welcome? Thank you!</p>
  
  <pre><code>SELECT PassA, (count(PassA(*)*100 / (Select count(*)FROM Grades} AS Total
  FROM Grades
  Group by PassA; 
  </code></pre>