SQLZOO：The JOIN operation

数据表：game-gaol-eteam

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

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

Q1

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'

Q2

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

SELECT id,stadium,team1,team2 FROM game
WHERE id='1012'

Q3

Show the player, teamid, stadium and mdate for every German goal.

SELECT player,teamid,stadium,mdate 
FROM game JOIN goal ON (id=matchid) 
WHERE teamid='GER'

JOIN

SQL JOIN 子句用于把来自两个或多个表的行基于共同字段结合

SQL INNER JOIN： 从多个表中返回满足 JOIN 条件的所有行

SELECT column1, column2, ...
FROM table1
JOIN table2 ON condition

INNER JOIN：如果表中有至少一个匹配，则返回行
LEFT JOIN：即使右表中没有匹配，也从左表返回所有的行
RIGHT JOIN：即使左表中没有匹配，也从右表返回所有的行
FULL JOIN：只要其中一个表中存在匹配，则返回行

Q4

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

SELECT team1,team2,player FROM game 
JOIN goal ON id=matchid
WHERE player LIKE 'Mario%'

Q5

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

SELECT player, teamid, coach,gtime 
FROM goal JOIN eteam ON id=teamid 
WHERE gtime<=10

Q6

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

SELECT mdate,teamname FROM game 
JOIN eteam ON team1=eteam.id
WHERE COACH='Fernando Santos'

Q7

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

SELECT player FROM game 
JOIN goal ON id=matchid 
WHERE stadium='National Stadium, Warsaw'

Q8

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.

SELECT DISTINCT player FROM game 
JOIN goal ON id=matchid 
WHERE teamid<>'GER'
AND (team1='GER' OR team2='GER')

Q9

Show teamname and the total number of goals scored.

SELECT teamname, COUNT(player) FROM eteam 
JOIN goal ON id=teamid 
GROUP BY teamname

Q10

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

SELECT stadium, COUNT(player) FROM game 
JOIN goal ON id=matchid 
GROUP BY stadium

Q11

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 matchid = id 
WHERE (team1 = 'POL' OR team2 = 'POL')
GROUP BY matchid

Q12

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

SELECT matchid,mdate,COUNT(teamid)
FROM goal JOIN game ON id=matchid
WHERE teamid='GER'
GROUP BY matchid

Q13

List every match with the goals scored by each team as shown. This will use "CASE WHEN"

SELECT 
mdate,
team1,
SUM(CASE WHEN teamid=team1 THEN 1 ELSE 0 END) as score1,
team2,
SUM(CASE WHEN teamid=team2 THEN 1 ELSE 0 END) as score2
FROM game LEFT JOIN goal ON id=matchid
GROUP BY mdate,matchid,team1,team2