What are the ids of stations that have latitude above 37.4 and never had bike availability below 7?
SELECT id FROM station WHERE lat  >  37.4 EXCEPT SELECT station_id FROM status GROUP BY station_id HAVING min(bikes_available)  <  7
stations with latitude above 37.4 refers to lat > 37.4; never had bike availability below 7 refers to MIN(bikes_available) >= 7;