What are the names for all the stations?
select name from station
What are the names for those serving "Ananthapuri Express" trains?
select t2.name from train_station as t1 join station as t2 on t1.station_id = t2.station_id join train as t3 on t3.train_id = t1.train_id where t3.name = "Ananthapuri Express"
How about those serving "Guruvayur Express"?
select t2.name from train_station as t1 join station as t2 on t1.station_id = t2.station_id join train as t3 on t3.train_id = t1.train_id where t3.name = "Guruvayur Express"
Which serve both?
select t2.name from train_station as t1 join station as t2 on t1.station_id = t2.station_id join train as t3 on t3.train_id = t1.train_id where t3.name = "Ananthapuri Express" intersect select t2.name from train_station as t1 join station as t2 on t1.station_id = t2.station_id join train as t3 on t3.train_id = t1.train_id where t3.name = "Guruvayur Express"