Self join Quiz

Link

1. Select the code that would show it is possible to get from Craiglockhart to Haymarket

SELECT DISTINCT a.name, b.name
  FROM stops a JOIN route z ON a.id=z.stop
  JOIN route y ON y.num = z.num
  JOIN stops b ON y.stop=b.id
 WHERE a.name='Craiglockhart' AND b.name ='Haymarket'

1. Select the code that shows the stops that are on route.num '2A' which can be reached with one bus from Haymarket?

SELECT S2.id, S2.name, R2.company, R2.num
  FROM stops S1, stops S2, route R1, route R2
 WHERE S1.name='Haymarket' AND S1.id=R1.stop
   AND R1.company=R2.company AND R1.num=R2.num
   AND R2.stop=S2.id AND R2.num='2A'

1. Select the code that shows the services available from Tollcross?

SELECT a.company, a.num, stopa.name, stopb.name  
FROM route a 
JOIN route b ON (a.company=b.company AND a.num=b.num)  
JOIN stops stopa ON (a.stop=stopa.id)  
JOIN stops stopb ON (b.stop=stopb.id) 
WHERE stopa.name='Tollcross'