Join opetation指的是不同的表之间通过某个相同的字段进行关联，从而进行查询操作。本文是对Join操作的小测

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练习

1. You want to find the stadium where player 'Dimitris Salpingidis' scored. Select the JOIN condition to use:

找到DS球员得分的体育场

select stadium 
from game
join goal on (id=matchid)
where player='Dimitris Salpingidis';

2. You JOIN the tables goal and eteam in an SQL statement. Indicate the list of column names that may be used in the SELECT line:

将goal和eteam表使用在SQL语句中，使用的字段可能有

matchid, teamid, player, gtime, id, teamname, coach

3. Select the code which shows players, their team and the amount of goals they scored against Greece(GRE).

找出和德国对抗中进球的数量

select player, teamid, count(*)
from game 
join goal on matchid=id
where (team1 = 'GRE' or team2 = 'GRE')   -- 两只球队中选择一只
and teamid != 'GRE'  -- 另一只球队不是GRE
group by player, teamid;   -- 分组显示

4. Select the result that would be obtained from this code

select distinct teamid, mdate   -- 结果中有两个字段
from goal
join game on (matchid=id)
where mdate='9 June 2012';   -- 指定特殊时间

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5. Select the code which would show the player and their team for those who have scored against Poland(POL) in National Stadium, Warsaw.

选择出和POL在该体育场中得分的player、teamid

select distinct player, teamid
from game join goal on matchid = id
where stadium = ' National Stadium, Warsaw'  -- 指定球场
and (team1 = 'POL' or team2 = 'POL')  -- 两支球队中有一只是波兰
and teamid != 'POL';  -- 另一只不是波兰

6. Select the code which shows the player, their team and the time they scored, for players who have played in Stadion Miejski (Wroclaw) but not against Italy(ITA).

找出在这个体育场中不是和ITA对抗的球队player、teamid、gtime

select distinct player, teamid, gtime
from game join goal on matchid = id
where stadium = 'Stadion Miejski (Wroclaw)'
and ((teamid = team2 and team1 != 'ITA') or (teamid = team1 and team2 != 'ITA'))   -- 只需要其中一个球队不是ITA，另外两个是一样的即可

7. Select the result that would be obtained from this code

select teamname, count(*)
from eteam 
join goal on
teamid=id
group by teamname   -- 分组
having count(*) < 3;  -- 过滤行

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