code: public function update_by()
      {
          $args = func_get_args();
          $data = array_pop($args);
  
          $data = $this->_do_pre_update($data);
  
          if ($data !== FALSE)
          {
              $this->_set_where($args);
              return $this->_update($data);
          }
  
          return FALSE;
      }
docs: Updated a record based on an arbitrary WHERE clause.