### 1. Write a query to find the names of the customers whose names are at least 15 characters long, and the second letter in the name is "l".
### Order by name.
queries[1]="""
select 0;
SELECT name
FROM customers
WHERE LENGTH(name) >= 15 AND name LIKE '_l%'
ORDER BY name;
"""
...
...
@@ -20,27 +23,71 @@ select 0;
### Order output by Customer Name.
### Output columns: all columns from customers
queries[2]="""
select 0;
WITH ids AS
(SELECT DISTINCT customers.customerid
FROM customers
INNER JOIN flewon ON customers.customerid = flewon.customerid
WHERE
EXTRACT(DAY FROM birthdate) = EXTRACT(DAY FROM flightdate)
AND
EXTRACT(MONTH FROM birthdate) = EXTRACT(MONTH FROM flightdate))
SELECT * FROM customers
WHERE customerid IN (SELECT * FROM ids)
ORDER BY name;
"""
### 3. Write a query to generate a list: (source_city, source_airport_code, dest_city, dest_airport_code, number_of_flights) for all source-dest pairs with at least 3 flights.
### Order first by number_of_flights in decreasing order, then source_city in the increasing order, and then dest_city in the increasing order.
### Note: You must generate the source and destination cities along with the airport codes.
queries[3]="""
select 0;
WITH source_airports AS
(
SELECT airportid AS source, city AS source_city FROM airports
),
dest_airports AS
(
SELECT airportid AS dest, city AS dest_city FROM airports
),
flight_counts AS
(
SELECT source_city, flights.source AS source_airport_code, dest_city, flights.dest AS dest_airport_code, COUNT(*) AS number_of_flights
FROM flights
INNER JOIN source_airports ON flights.source = source_airports.source
INNER JOIN dest_airports ON flights.dest = dest_airports.dest
GROUP BY source_city, flights.source, dest_city, flights.dest
)
SELECT *
FROM flight_counts
WHERE number_of_flights >= 3
ORDER BY number_of_flights DESC, source_city ASC, dest_city ASC;
"""
### 4. Find the name of the airline with the maximum number of customers registered as frequent fliers.
### Output only the name of the airline. If multiple answers, order by name.
queries[4]="""
select 0;
WITH frequent_fliers_counts AS
(SELECT frequentflieron AS airlineid, COUNT(*) AS count FROM customers GROUP BY frequentflieron)
SELECT name
FROM airlines
INNER JOIN frequent_fliers_counts ON airlines.airlineid = frequent_fliers_counts.airlineid
WHERE count = (SELECT MAX(count) FROM frequent_fliers_counts)
ORDER BY name;
"""
### 5. For all flights from OAK to IAD, list the flight id, airline name, and the
### duration in hours and minutes. So the output will have 4 fields: flightid, airline name,
### hours, minutes. Order by flightid.
queries[5]="""
select 0;
WITH flights_with_times AS
(
SELECT flightid, airlineid, local_arrival_time - local_departing_time AS elapsed
FROM flights
WHERE source = 'OAK' AND dest = 'IAD'
)
SELECT flightid, name AS airline_name, EXTRACT(HOUR FROM elapsed) AS hours, EXTRACT(MINUTE FROM elapsed) AS minutes
FROM flights_with_times
INNER JOIN airlines ON flights_with_times.airlineid = airlines.airlineid
ORDER BY flightid;
"""
### 6. Write a query to find empty flights (flight, flight date) on any date
...
...
@@ -48,7 +95,14 @@ select 0;
### flights took off as scheduled, with or without passengers. Order by flight
### id in increasing order, and then by date in increasing order.
queries[6]="""
select 0;
WITH valid_dates AS
(SELECT DISTINCT flightdate FROM flewon),
all_flights AS
(SELECT flightid, flightdate FROM flights CROSS JOIN valid_dates)
SELECT flightid, flightdate
FROM all_flights
EXCEPT (SELECT DISTINCT flightid, flightdate FROM flewon)
ORDER BY flightid ASC, flightdate ASC;
"""
### 7. Write a query to generate a list of customers who don't list Southwest as their frequent flier airline, but
...
...
@@ -56,15 +110,45 @@ select 0;
### Output columns: customerid, customer_name
### Order by: customerid
queries[7]="""
select 0;
WITH flewon_airline AS
(
SELECT customerid, airlineid FROM flewon INNER JOIN flights ON flewon.flightid = flights.flightid
),
flewon_airline_count AS
(
SELECT customerid, airlineid, COUNT(*) AS num_flights FROM flewon_airline GROUP BY customerid, airlineid
),
max_flights AS
(
SELECT customerid, MAX(num_flights) AS most_flown FROM flewon_airline_count GROUP BY customerid
),
preferred_airline AS
(
SELECT flewon_airline_count.customerid, airlineid
FROM flewon_airline_count
INNER JOIN max_flights ON flewon_airline_count.customerid = max_flights.customerid
WHERE num_flights = most_flown
ORDER BY flewon_airline_count.customerid
)
SELECT preferred_airline.customerid, name AS customer_name
FROM preferred_airline
INNER JOIN customers ON preferred_airline.customerid = customers.customerid
WHERE airlineid = 'SW' AND frequentflieron != 'SW'
ORDER BY customerid;
"""
### 8. Write a query to generate a list of those customers whose first and last flights are 5 days apart.
### 8. Write a query to generate a list of customers where the interval between first and last flight is 5 days.
### Order by the customer name.
### Output columns: name
### Order by: name
queries[8]="""
select 0;
WITH intervals AS
(SELECT customerid, MAX(flightdate) - MIN(flightdate) AS interval FROM flewon GROUP BY customerid)
SELECT name
FROM intervals
INNER JOIN customers ON intervals.customerid = customers.customerid
WHERE interval = 5
ORDER BY name;
"""
...
...
@@ -73,7 +157,16 @@ select 0;
### Output columns: customerid, airlinename
### Order by: customerid, airlinename
queries[9]="""
select 0;
WITH never_flown_on AS
(
SELECT customerid, airlineid
FROM customers CROSS JOIN airlines
EXCEPT (SELECT DISTINCT customerid, airlineid FROM flewon INNER JOIN flights ON flewon.flightid = flights.flightid)
)
SELECT customerid, name AS airlinename
FROM never_flown_on
INNER JOIN airlines ON never_flown_on.airlineid = airlines.airlineid
ORDER BY customerid, airlinename;
"""
...
...
@@ -83,7 +176,18 @@ select 0;
### Output columns: name,coupon
### Order by: name,coupon
queries[10]="""
select 0;
WITH ids AS
(SELECT DISTINCT customers.customerid
FROM customers
INNER JOIN flewon ON customers.customerid = flewon.customerid
WHERE
EXTRACT(DAY FROM birthdate) = EXTRACT(DAY FROM flightdate)
AND
EXTRACT(MONTH FROM birthdate) = EXTRACT(MONTH FROM flightdate))
SELECT name, SUBSTRING(name for 3) || EXTRACT(DAY FROM birthdate) AS coupon
