Fixed #20168 - Generalized a PostgreSQL specific database query in the docs.

                SELECT p.id, p.question, p.poll_date, COUNT(*)

                FROM polls_opinionpoll p, polls_response r

                WHERE p.id = r.poll_id

                GROUP BY 1, 2, 3

                ORDER BY 3 DESC""")

                GROUP BY p.id, p.question, p.poll_date

                ORDER BY p.poll_date DESC""")

            result_list = []

            for row in cursor.fetchall():

                p = self.model(id=row[0], question=row[1], poll_date=row[2])