title: show NULL and values
body: <p>I've got three table where I've got field - <code>area</code>. So I decided to find sum of areas for every table and show it in one view.</p>
  
  <p>I've created a query </p>
  
  <pre><code>select sum(x.area) as EquipmentSpace,sum(y.area) as ProductSpace,sum(z.area) as ShoppointSpace
  from TEquipWarehouse as x,TProductWarehouse as y,TShopPoint as z
  </code></pre>
  
  <p>However when one of tables doesn't have any record - the results of every field are <code>NULL</code>.</p>
  
  <p>How to solve this problem?</p>