title: mysql SUM of VARCHAR fields without using CAST
body: <p>When SUM is used in query on field of type VARCHAR in MySql database, does SUM automatically convert it into number ?
  I tried this by using</p>
  
  <pre><code>  SELECT SUM(parametervalue) FROM table
  </code></pre>
  
  <p>and it reveals that MySql returns the sum although I expected to throw it an error as "parametervalue" field is of VARCHAR type</p>