sqlzoo习题答案--Self join

Details of the database Looking at the data

stops(id, name)
route(num,company,pos, stop)

stops	route
id	num
name	company
	pos
	stop

1.How many stops are in the database.

select count(id) from stops

2.Find the id value for the stop 'Craiglockhart'

select id from stops
where name='Craiglockhart'

3.Give the id and the name for the stops on the '4' 'LRT' service.

select id,name
from stops join route
on stops.id=route.stop
where num='4' and company='LRT'

4.The query shown gives the number of routes that visit either London Road (149) or Craiglockhart (53). Run the que