title: Average of Average in one row
body: <p>I'm not sure if this is possible what I'm trying to achieve. I want to get the avg of averaged columns. </p>
  
  <pre><code>SELECT avg(col1), avg(col2), avg(col3) FROM tbl
  </code></pre>
  
  <p>My Result should be the avg of all three avg columns, is this possible? Something like this</p>
  
  <pre><code>SELECT avg( col1, col2, col3) FROM tbl
  </code></pre>
  
  <p>doesn't work at MySQL 5.1</p>