How many trips made by a subscriber started in August, 2013 from a station that can hold more than 20 bikes?
subscriber refers to subscription_type = 'Subscriber'; in August 2013 refers to start_date LIKE'8%' AND start_date LIKE'%2013%'; station that can hold more than 20 bikes refers to dock_count>20;
SELECT COUNT(T2.id) FROM station AS T1 INNER JOIN trip AS T2 ON T1.id = T2.start_station_id WHERE T2.subscription_type = 'Subscriber' AND T2.start_date LIKE '8/%/2013%' AND T1.dock_count > 20