title: PHP/mysql getting average value of a table column
body: <p>How do you get the everage of a mysql table column?</p>
  
  <p>for example:</p>
  
  <pre><code>id | name | age
  
  0 | name1 | 20
  1 | name2 | 33
  2 | name3 | 18
  3 | name4 | 24
  </code></pre>
  
  <p>I want to get the average of all the ages. </p>