SQLZOO练习5--join（表的连接）

game表：

id	mdate	stadium	team1	team2
1001	8 June 2012	National Stadium, Warsaw	POL	GRE
1002	8 June 2012	Stadion Miejski (Wroclaw)	RUS	CZE
1003	12 June 2012	Stadion Miejski (Wroclaw)	GRE	CZE
1004	12 June 2012	National Stadium, Warsaw	POL	RUS
……

goal表：

matchid	teamid	player	gtime
1001	POL	Robert Lewandowski	17
1001	GRE	Dimitris Salpingidis	51
1002	RUS	Alan Dzagoev	15
1002	RUS	Roman Pavlyuchenko	82
……

team表：

id	teamname	coach
POL	Poland	Franciszek Smuda
RUS	Russia	Dick Advocaat
CZE	Czech Republic	Michal Bilek
GRE	Greece	Fernando Santos
……

1、获取德国的比赛id和参赛人员。

The first example shows the goal scored by a player with the last name 'Bender'. The * says to list all the columns in the table - a shorter way of saying matchid, teamid, player, gtime

Modify it to show the matchid and player name for all goals scored by Germany. To identify German players, check for: teamid = 'GER'

SELECT matchid,player
FROM goal
WHERE teamid = 'GER';

2、Show id, stadium, team1, team2 for just game 1012

From the previous query you can see that Lars Bender's scored a goal in game 1012. Now we want to know what teams were playing in that match.

Notice in the that the column matchid in the goal table corresponds to the id column in the game table. We can look up information about game 1012 by finding that row in the game table.

Show id, stadium, team1, team2 for just game 1012

SELECT id,stadium,team1,team2
  FROM game
where id=1012;

3、Modify it to show the player, teamid, stadium and mdate for every German goal.

You can combine the two steps into a single query with a JOIN.

SELECT *
  FROM game JOIN goal ON (id=matchid)

The FROM clause says to merge data from the goal table with that from the game table. The ON says how to figure out which rows in game go with which rows in goal - the matchid from goal must match id from game. (If we wanted to be more clear/specific we could say
ON (game.id=goal.matchid)

The code below shows the player (from the goal) and stadium name (from the game table) for every goal scored.

Modify it to show the player, teamid, stadium and mdate for every German goal.

SELECT goal.player,goal.teamid,game.stadium,game.mdate
from goal
left join
game
on goal.matchid=game.id
where goal.teamid='GER';

4、Show the team1, team2 and player for every goal scored by a player called Mario player LIKE 'Mario%'

Use the same JOIN as in the previous question.

select game.team1,game.team2,goal.player
from game
left join
goal
on game.id=goal.matchid
where goal.player like'Mario%';

5、Show player, teamid, coach, gtime for all goals scored in the first 10 minutes gtime<=10

The table eteam gives details of every national team including the coach. You can JOIN goal to eteam using the phrase goal JOIN eteam on teamid=id

select goal.player,goal.teamid,eteam.coach,goal.gtime
from goal
join eteam
on goal.teamid=eteam.id
where goal.gtime<=10;

6、List the dates of the matches and the name of the team in which 'Fernando Santos' was the team1 coach.

To JOIN game with eteam you could use either

game JOIN eteam ON (team1=eteam.id) or game JOIN eteam ON (team2=eteam.id)

Notice that because id is a column name in both game and eteam you must specify eteam.id instead of just id

select game.mdate,eteam.teamname
from game
join
eteam
on game.team1=eteam.id
where eteam.coach='Fernando Santos';

7、List the player for every goal scored in a game where the stadium was 'National Stadium, Warsaw'

select goal.player
from goal
join game
on goal.matchid=game.id
where game.stadium='National Stadium, Warsaw';

8、The example query shows all goals scored in the Germany-Greece quarterfinal.

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

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

select eteam.teamname,count(teamid)
from eteam
join goal
on eteam.id=goal.teamid
group by teamname;

10、Show the stadium and the number of goals scored in each stadium.

select game.stadium,count(teamid)
from game
join goal
on game.id=goal.matchid
group by stadium;

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

SELECT goal.matchid,game.mdate, COUNT(player) from goal join game on goal.matchid=game.id where team1 LIKE '%POL%' or team2 LIKE '%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 goal.matchid,game.mdate,count(player)
from goal
join game
on goal.matchid=game.id
where teamid LIKE'%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.

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 game.mdate,game.team1,
sum(case when teamid=team1 then 1 else 0 end) as score1,
game.team2,
sum(case when teamid=team2 then 1 else 0 end) as score2
from game
left join goal
on game.id=goal.matchid
group by mdate,matchid,team1,team2;

解题思路：

️game表和goal表的连接

️case when，判断，来得出score1，score2。