title: How to delete all rows that have NOT NULL in one specific column?
body: <p>Im trying to delete all rows that have a value in the column ' toevoeging '</p>
  
  <p>I made this query: </p>
  
  <pre><code>DELETE FROM gebruiksoppervlakte WHERE toevoeging = NOT NULL;
  </code></pre>
  
  <p>Why is this not possible? 
  So I want to keep the rows that have NULL
  Thanks!</p>