example of average cost per minute of flights involving various airports

example.sql

sqlite> # departure_airport, arrival_airport, cost (EUR), travel_time (minutes)
sqlite> SELECT * FROM flights;AMS|KBP|329|170
AMS|OTP|308|165
BRU|KBP|70|165
BRU|OTP|110|165
CDG|KBP|201|185
CDG|OTP|160|170
CDG|AMS|588|80
CDG|BRU|287|55
KBP|AMS|423|185
KBP|CDG|293|205
KBP|BRU|191|185
OTP|AMS|229|180
OTP|BRU|313|170
sqlite> # airport, # of flights involving that airport, average cost per minute of flights involving that airport
sqlite> SELECT airport, COUNT(COST), SUM(COST)*1.0/SUM(travel_time) AS avg_cost_per_minute  FROM (SELECT departure_airport AS airport, cost, travel_time FROM flights UNION ALL SELECT arrival_airport AS airport, cost, travel_time FROM flights) GROUP BY airport ORDER BY avg_cost_per_minute;
BRU|5|1.31216216216216
OTP|5|1.31764705882353
KBP|6|1.37625570776256
CDG|5|2.2
AMS|5|2.40641025641026