title: UPDATE row relative to CURRENT_TIMESTAMP is not giving the correct value
body: <p>I am trying to update a MySQL table with an 'expiration date'. I've collected a timestamp value for all my rows as people have registered into the table but now I want to create an expiration date relative to that timestamp (not to relative to the current time). Here's my code:</p>
  
  <pre><code>$timestamp = $row['timestamp'];
  $sql_update = "
  UPDATE jobs
  SET expiration_date = DATE_ADD('$timestamp',INTERVAL 56 DAY)";
  $result_update = $mysqli-&gt;query($sql_update) or die($mysqli-&gt;error);
  </code></pre>
  
  <p>Understand that this is being run in a 'while' loop so it's running through each row of the table an updating them as it goes. The issue is that I ran it once and all it did was update the 'expiration_date' row to 56 days from NOW not 56 days from the timestamp's value. The timestamp is set on CURRENT_TIMESTAMP for when the a new entry is registered which I'm assuming is the problem. I've echoed out $timestamp to troubleshoot and it echoes out the correct value (not the current time) when I echo it but when it goes to actually update the expiration date it seems to be drawing from the fact that it's a CURRENT_TIMESTAMP. Is there a way to explicit query for the value of the timestamp?</p>
  
  <p>I'm hoping to find a way that doesn't involved restructuring the database. I know I could have it so instead of a timestamp row, I could make it a datetime row and set it to the value of NOW() when database is being initially queried to add a row but I'd prefer to find a solution within the way the table is currently set up. Thanks!</p>