title: SQL minus 2 columns - with null values
body: <p>I have this table (made from a SQL query):</p>
  
  <pre><code>Row 1 Row 2 
  2     1    
  3     NULL 
  </code></pre>
  
  <p>And I want to minus the 2 columns, so I just select like this:</p>
  
  <pre><code>Select Row1 - Row2
  From table
  </code></pre>
  
  <p>But then I get this result:</p>
  
  <pre><code>1
  NULL
  </code></pre>
  
  <p>instead of:</p>
  
  <pre><code>1
  3
  </code></pre>
  
  <p>How can I make it possible to get the last result?</p>