title: Calculating the ratio of each item to the column in SQL
body: <p>I have a data like this:</p>
  <pre><code>col1 value
  A     2
  B     4
  C     8   
  D     6
  </code></pre>
  <p>I want to calculate the ratios to the column total</p>
  <pre><code>col1 value
  A     10%
  B     20%
  C     40% 
  D     30%
  </code></pre>
  <p>How can I do this with SQL?</p>