title: Only insert data WHERE NOT EXISTS not working
body: <p>How can I change this query to only insert the information, if the information is not already there?</p>
  
  <p>I've tried adding WHERE NOT EXISTS, but it stops the query working. Can anyone help me out, maybe I'm typing it wrong.</p>
  
  <pre><code>$sql = "UPDATE tbl_blocking SET active = '0' WHERE blocking = :user AND user = :who LIMIT 1";
  </code></pre>