sqlzoo习题答案--The join operation

8.show the name of all players who scored a goal against Germany.

HINT

Select goals scored only by non-German players in matches where GER was the id of either team1 or team2.

You can use teamid!='GER' to prevent listing German players.

You can use DISTINCT to stop players being listed twice.

SELECT distinct player
   from goal join game
   on(game.id=goal.matchid)
   where teamid!='GER' and (team1='GER' or team2='GER')

9.Show teamname and the total number of goals scored.

SELECT teamname, count(teamid)
   FROM eteam JOIN goal
   ON eteam.id=goal.teamid
   group BY teamname

11.For every match involving 'POL', show the matchid, date and the number of goals scored.

SELECT matchid,mdate, count(teamid)
   FROM game JOIN goal
   ON (game.id= goal.matchid)
   WHERE (team1 = 'POL' OR team2 = 'POL')
   group by matchid,mdate

12.For every match where 'GER' scored, show matchid, match date and the number of goals scored by 'GER'

select matchid,mdate,count(teamid)
   from game join goal
   on(game.id=goal.matchid)
   where teamid='GER'
   group by matchid,mdate

13.List every match with the goals scored by each team as shown. This will use "CASE WHEN" which has not been explained in any previous exercises.

mdate	team1	score1	team2	score2
1 July 2012	ESP	4	ITA	0
10 June 2012	ESP	1	ITA	1
10 June 2012	IRL	1	CRO	3
...

Notice in the query given every goal is listed. If it was a team1 goal then a 1 appears in score1, otherwise there is a 0. You could SUM this column to get a count of the goals scored by team1. Sort your result by mdate, matchid, team1 and team2.

SELECT mdate,team1,     
    SUM(CASE  WHEN teamid=team1 THEN 1  
              ELSE 0 END) score1,     
    team2,     
    SUM(CASE  WHEN teamid=team2 THEN 1         
              ELSE 0 END) score2     
    FROM game left JOIN goal ON matchid = id 
    group by mdate, matchid, team1,team2