sql-tutorial/recursion.sql at master · crutch/sql-tutorial · GitHub

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CREATETABLEcities (
 id SERIALNOT NULLPRIMARY KEY,
 name TEXT
);

CREATETABLEflights (
 id SERIALNOT NULLPRIMARY KEY,
 from_city INTEGERREFERENCES cities(id),
 to_city INTEGERREFERENCES cities(id)
);


INSERT INTO cities(name) VALUES
('Vienna'),
('Paris'),
('Boston'),
('New York'),
('Tokyo'),
('Dubai'),
('Sydney'),
('Singapore'),
('London'),
('San Francisco'),
('Los Angeles');

INSERT INTO flights(from_city, to_city) VALUES
(1,2),
(2,3),
(2,4),
(7,5),
(7,11),
(7,10),
(5,8),
(8,7),
(1,9),
(3,4),
(1,6);

INSERT INTO flights(from_city, to_city) VALUES
(4,2);

WITH RECURSIVE connections(from_city, to_city, stops, via) AS (
SELECT from_city, to_city, 0, ''FROM flights
UNION ALL
SELECTconns.from_city, fl.to_city, conns.stops+1, conns.via||'==>'||cfr.name||'==>'
FROM connections conns
JOIN flights fl ONconns.to_city=fl.from_city
JOIN cities cfr ONcfr.id=fl.from_city
WHEREconns.from_city!=fl.to_cityANDconns.stops<4
) SELECTfrom_c.name, via , to_c.name, stops FROM connections c
JOIN cities from_c ONfrom_c.id=c.from_city
JOIN cities to_c ONto_c.id=c.to_city
WHEREfrom_c.name='Vienna';


WITH RECURSIVE connections(from_city, to_city, stops, via) AS (
SELECT from_city, to_city, 0, ARRAY[]::text[] FROM flights
UNION ALL
SELECTconns.from_city, fl.to_city, conns.stops+1, array_append(conns.via, cfr.name)
FROM connections conns
JOIN flights fl ONconns.to_city=fl.from_city
JOIN cities cfr ONcfr.id=fl.from_city
WHEREconns.from_city!=fl.to_cityANDconns.stops<4AND NOT(ARRAY[cfr.name]::text[] <@ via)
) SELECTfrom_c.name, via , to_c.name, stops FROM connections c
JOIN cities from_c ONfrom_c.id=c.from_city
JOIN cities to_c ONto_c.id=c.to_city
WHEREfrom_c.name='Vienna';