### Database Schema:
CREATE TABLE status (
	station_id	INTEGER	NULL,
	bikes_available	INTEGER	NULL,
	docks_available	INTEGER	NULL,
	time	TEXT	NULL
);

CREATE TABLE station (
	id	INTEGER	NOT NULL	PRIMARY KEY,
	name	TEXT	NULL,
	lat	REAL	NULL,
	long	REAL	NULL,
	dock_count	INTEGER	NULL,
	city	TEXT	NULL,
	installation_date	TEXT	NULL
);

CREATE TABLE weather (
	date	TEXT	NULL,
	max_temperature_f	INTEGER	NULL,
	mean_temperature_f	INTEGER	NULL,
	min_temperature_f	INTEGER	NULL,
	max_dew_point_f	INTEGER	NULL,
	mean_dew_point_f	INTEGER	NULL,
	min_dew_point_f	INTEGER	NULL,
	max_humidity	INTEGER	NULL,
	mean_humidity	INTEGER	NULL,
	min_humidity	INTEGER	NULL,
	max_sea_level_pressure_inches	REAL	NULL,
	mean_sea_level_pressure_inches	REAL	NULL,
	min_sea_level_pressure_inches	REAL	NULL,
	max_visibility_miles	INTEGER	NULL,
	mean_visibility_miles	INTEGER	NULL,
	min_visibility_miles	INTEGER	NULL,
	max_wind_Speed_mph	INTEGER	NULL,
	mean_wind_speed_mph	INTEGER	NULL,
	max_gust_speed_mph	INTEGER	NULL,
	precipitation_inches	TEXT	NULL,
	cloud_cover	INTEGER	NULL,
	events	TEXT	NULL,
	wind_dir_degrees	INTEGER	NULL,
	zip_code	TEXT	NULL
);

CREATE TABLE trip (
	id	INTEGER	NOT NULL	PRIMARY KEY,
	duration	INTEGER	NULL,
	start_date	TEXT	NULL,
	start_station_name	TEXT	NULL,
	start_station_id	INTEGER	NULL,
	end_date	TEXT	NULL,
	end_station_name	TEXT	NULL,
	end_station_id	INTEGER	NULL,
	bike_id	INTEGER	NULL,
	subscription_type	TEXT	NULL,
	zip_code	INTEGER	NULL
);

### User's Query:
Among the subscriber, how many of them finished the 2nd at Folsom and Civic Center BART (7th at Market) as their start and end stations respectively for no more than 490 seconds under minimum visibility of 4 miles.

### Extra Knowledge:
subscription_type = 'Subscriber'; no more than 490 seconds refers to duration<490; start_station_name = '2nd at Folsom'; end_station_name = 'Civic Center BART (7th at Market)'; min_visibility_miles = 4;
SELECT COUNT(T1.id) FROM trip AS T1 INNER JOIN weather AS T2 ON T2.zip_code = T1.zip_code WHERE T1.subscription_type = 'Subscriber' AND T2.min_visibility_miles = 4 AND T1.duration < 490 AND T1.start_station_name = '2nd at Folsom' AND T1.end_station_name = 'Civic Center BART (7th at Market)'