title: MySQL: The correct way to calculate standard deviation
body: <p>I have the weight of different people.</p>
  
  <p>The average is:</p>
  
  <pre><code>select avg(weight) as avg_weight
  from table;
  </code></pre>
  
  <p>But what's the difference between <code>stddev()</code> and <code>std()</code>?  Is it possible to get the standard deviation from avg_weight?</p>
  
  <p>Is this the correct way:</p>
  
  <pre><code>select stddev(weight)
  from table;  /* -&gt; is here where the function avg(weight) included? */
  </code></pre>
  
  <p>Or do I need something like this:</p>
  
  <pre><code>select stddev(avg(weight))
  from table;  /* (but this does not work) */
  </code></pre>
  
  <p>Thanks.</p>