title: Change the value of one column based on the value of another column
body: <p>Lets say i have a table like so...</p>
  
  <pre><code>ITEM#     ItemType     SIZE
  1         Car          5.20
  2         Watch        2.00
  3         Watch        7.50
  4         Watch        6.40
  5         Car          5.00
  6         Car          4.30
  </code></pre>
  
  <p>I would like to select all rows but whenever the ItemType = 'Car' I would like the value for SIZE to be returned as null.</p>
  
  <p>I have tried using</p>
  
  <pre><code>CASE When ItemType = 'Car'
  Then SIZE = null
  END
  </code></pre>
  
  <p>but this does not work.</p>
  
  <p>Many thanks!</p>