title: Compare when value could be both NULL or text
body: <p>Now I know you can't directly compare NULL to anything (as null is unknown) so how would I achieve the following:</p>
  
  <pre><code>select  *
      from    Material as m
      where   MtrlCode = 826 and
              Exposlimit &lt;&gt; 'compareMe'
  </code></pre>
  
  <p>Where Exposlimit MAY be NULL or it may not be.
  'compareMe' may also be NULL.</p>
  
  <p>Therefore how do I compare the two?  Both sides could be either text or NULL.</p>