有什么问题，欢迎评论或私聊。转载请私聊博主，谢谢。

原题链接：https://sqlzoo.net/wiki/The_JOIN_operation

其他题解连接：https://blog.csdn.net/aiqiyizz/article/details/109057732

题解对应的是英文版题目。

从JOIN开始应该是难度的分水岭了。

文章目录

6 JOIN
- 6.1
- 6.2
- 6.3
- 6.4
- 6.5
- 6.6
- 6.7
- 6.8 More difficult questions
- 6.9
- 6.10
- 6.11
- 6.12
- 6.13

6 JOIN

6.1

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

6.2

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

6.3

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

6.4

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

6.5

前几道题题目没看清就做都对。。

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

6.6

迷惑题意*1

本来以为要输出的是比赛名字和对手队名

SELECT mdate, y.teamname
FROM game JOIN eteam x ON game.team1 = x.id
     JOIN eteam y ON game.team2 = y.id
WHERE x.coach = 'Fernando Santos'

最后发现要输出的是比赛名字和自己队名

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

6.7

该题正解有问题，应该添加DISTINCT。

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

6.8 More difficult questions

DISTINCT用于排除重复项，WHERE前部分条件排除德国人，第二部分限制与德国对战条件。

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

6.9

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

6.10

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

6.11

SELECT matchid, mdate, COUNT(teamid)
  FROM game JOIN goal ON matchid = id 
 WHERE (team1 = 'POL' OR team2 = 'POL')
 GROUP BY matchid, mdate

6.12

SELECT matchid, mdate, COUNT(teamid)
  FROM game JOIN goal ON matchid = id 
 WHERE teamid = 'GER' AND (team1 = 'GER' OR team2 = 'GER')
 GROUP BY matchid, mdate

6.13

题意怪，看了一会才捕捉到关键词，需要形成题目要求的表格。

主要要使用game LEFT JOIN goal ON matchid = id

因为存在一场比赛两队都没有得分的情况，这样在game中存在id而在goal中不存在matchid。使用JOIN不会加入表格。

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

sqlzoo 6.JOIN 答案