Display queries holding locks other queries are waiting to be
        released.

        Record(
            pid=40821,
            source='',
            running_for=datetime.timedelta(0, 0, 2857),
            waiting=False,
            query='SELECT pg_sleep(10);'
        )

        :returns: list of Records

def blocking(self):
        """
        Display queries holding locks other queries are waiting to be
        released.

        Record(
            pid=40821,
            source='',
            running_for=datetime.timedelta(0, 0, 2857),
            waiting=False,
            query='SELECT pg_sleep(10);'
        )

        :returns: list of Records
        """

        return self.execute(
            sql.BLOCKING.format(
                query_column=self.query_column,
                pid_column=self.pid_column
            )
        )