title: Remove negative values
body: <p>I have a certain query that obtains derived values </p>
  
  <pre><code>select datediff(minute, date_field_1, date_field_2) as date_diff from table_name;
  </code></pre>
  
  <p>The problem is that some of the values in the result can be negative as <code>date_field_1</code> can be greater than <code>date_field_2</code> in some cases.</p>
  
  <p>So this results in negative, along with positive values in the resultant table.</p>
  
  <p>Is there anyway to put some default values or omit and give null or zero in those negative calculated values ?</p>
  
  <p>Using redshift.</p>