SELECT COUNT(*) FROM subzones WHERE population > 15000; SELECT max_floor, COUNT(max_floor) FROM hdb_blocks GROUP BY max_floor ORDER BY COUNT(max_floor) desc LIMIT 1; SELECT * FROM areas a WHERE region = 'central' AND NOT EXISTS ( SELECT 1 FROM mrt_stations m,subzones s WHERE m.subzone = s.name AND s.area = a.name ); SELECT sz.area, COUNT(stop.code) AS num_stops FROM mrt_stops stop, mrt_stations s, subzones sz WHERE stop.station = s.name AND s.subzone = sz.name GROUP BY sz.area ORDER BY num_stops DESC LIMIT 3; SELECT DISTINCT m1.station FROM mrt_connections c, mrt_stops m1, mrt_stops m2 WHERE c.from_code = m1.code AND c.to_code = m2.code AND m1.line = 'ew' AND m2.line != 'ew'; SELECT sz.area, COUNT(DISTINCT so.line) AS num_lines FROM mrt_stops so, mrt_stations st, subzones sz WHERE so.station = st.name AND st.subzone = sz.name GROUP BY sz.area HAVING COUNT(DISTINCT so.line) >= 3 ORDER BY num_lines DESC; SELECT tab.area, COUNT(*) AS num_lines FROM ( SELECT s.area, h.line FROM mrt_stops h, mrt_stations m, subzones s WHERE h.station = m.name AND m.subzone = s.name GROUP BY s.area, h.line ) tab GROUP BY tab.area HAVING COUNT (*) >= 3 ORDER BY num_lines DESC