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Update self_join.sql #1

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70 changes: 10 additions & 60 deletions self_join.sql
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Original file line number Diff line number Diff line change
Expand Up @@ -107,72 +107,22 @@ WHERE S1.name='Craiglockhart'


-- 10.
-- Find the routes involving two buses that can go from Craiglockhart to Sighthill.
-- Find the routes involving two buses that can go from Craiglockhart to Lochend.
-- Show the bus no. and company for the first bus, the name of the stop for the transfer,
-- and the bus no. and company for the second bus.

-- Hint
-- Self-join twice to find buses that visit Craiglockhart and Sighthill, then join those on matching stops.


SELECT DISTINCT a.num, a.company, stopb.name , c.num, c.company
FROM route a JOIN route b
ON (a.company = b.company AND a.num = b.num)
JOIN ( route c JOIN route d ON (c.company = d.company AND c.num= d.num))
JOIN stops stopa ON (a.stop = stopa.id)
JOIN stops stopb ON (b.stop = stopb.id)
JOIN stops stopc ON (c.stop = stopc.id)
JOIN stops stopd ON (d.stop = stopd.id)
WHERE stopa.name = 'Craiglockhart' AND stopd.name = 'Sighthill'
AND stopb.name = stopc.name
ORDER BY LENGTH(a.num), b.num, stopb.id, LENGTH(c.num), d.num
;












































-- Self-join twice to find buses that visit Craiglockhart and Lochend, then join those on matching stops.


SELECT r1.num, r1.company, s2.name, r3.num, r3.company FROM route r1

JOIN route r2 ON r2.num = r1.num AND r2.company = r1.company
JOIN ( route r3 JOIN route r4 ON r3.num = r4.num AND r3.company = r4.company ) ON r2.stop = r3.stop

JOIN stops s1 ON r1.stop = s1.id
JOIN stops s2 ON r2.stop = s2.id
JOIN stops s3 ON r3.stop = s3.id
JOIN stops s4 ON r4.stop = s4.id

WHERE s1.name = 'Craiglockhart' AND s4.name = 'Lochend'