Update same table using dynamic query in drupal 7
To execute clauses like that you would use a where funtion. so your code would be something like

$query = db_update('books','pb');
$query-&gt;fields($update_values);
$query-&gt;where("b.pdays * (36400) + b.ptime_from &gt; 6546");
$isbn_reds = $query-&gt;execute();