title: StDev() function returns Null when table contains only one row
body: <p>I am trying to use the StDev function and am getting blank results. I am using it as...</p>
  
  <pre><code>SELECT StDev(fldMean) FROM myTable
  </code></pre>
  
  <p>Where fldMean contains a value of 2.3 and should evaluate to 0 but instead I am simply getting an empty result. I can't seem to understand how expressions are to be used in the function, Microsoft's manual really didn't help.</p>