code: public function one($db = null)
      {
          if ($this->emulateExecution) {
              return false;
          }
  
          return $this->createCommand($db)->queryOne();
      }
docs: Executes the query and returns a single row of result.
  @param Connection $db the database connection used to generate the SQL statement.
  If this parameter is not given, the `db` application component will be used.
  @return array|bool the first row (in terms of an array) of the query result. False is returned if the query
  results in nothing.