title: How join columns with null value?
body: <p><strong>Hi please help me. How join 3 columns with null values?.</strong></p>
  
  <pre><code>SELECT [item],[Prox],[z], [item]+[Prox]+[z] as result FROM [FIELD$];
  </code></pre>
  
  <p><strong>Result.</strong></p>
  
  <p><img src="https://i.stack.imgur.com/JFUQh.png" alt=""></p>