Update query with a dynamic expression in Drupal 7?
You want to use an expression: http://api.drupal.org/api/drupal/includes--database--query.inc/function/UpdateQuery%3A%3Aexpression/7

Example:

db_update('warrior_members')
  -&gt;expression('points', 'points + 1')
  -&gt;condition('uid', $liv_user)
  -&gt;execute();


Or to make the 1 dynamic:

db_update('warrior_members')
  -&gt;expression('points', 'points + :amount', array(':amount' =&gt; 1))
  -&gt;condition('uid', $liv_user)
  -&gt;execute();