code: public function has($uid) {
          $options = $this->getOptions();
          $stmt = $this->adapter->query(sprintf('SELECT %s FROM %s WHERE %s = "%s"', $options['column_value'], $options['table'], $options['column_key'], $uid), Adapter::QUERY_MODE_EXECUTE);
          return $stmt->count() > 0;
      }
docs: Test if has datas with $uid key
  @param mixed $uid
  @return boolean