title: update column with comma separated value
body: <p>In my SQL table, I have a column named "user_id" with comma separated value like this: a,b,c,d and I just wonder how can I update this column without removing old values. I want to update this column to a,b,c,d,e and in other step to a,b,c,d,e,f.</p>
  
  <p>I wrote this query, but it removes old values and does not not update values with comma separated list:</p>
  
  <pre><code>UPDATE multiusers SET user_id = '" . $userID . "' WHERE hwid = '" . $hwid."' 
  </code></pre>