The JOIN operation/zh

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game(賽事)
id(編號) mdate(日期) stadium(場館) team1(隊伍1) team2(隊伍2)
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(入球)
matchid(賽事編號) teamid(隊伍編號) player(入球球員) gtime(入球時間)
1001 POL Robert Lewandowski 17
1001 GRE Dimitris Salpingidis 51
1002 RUS Alan Dzagoev 15
1001 RUS Roman Pavlyuchenko 82
...


eteam(歐洲隊伍)
id(編號) teamname(隊名) coach(教練)
POL Poland Franciszek Smuda
RUS Russia Dick Advocaat
CZE Czech Republic Michal Bilek
GRE Greece Fernando Santos
...


合拼表格-- 歐洲國家盃 UEFA EURO 2012

此教程是介召 JOIN的使用,讓你合拼2個或更多的表格。數據庫的表格貯存了在波蘭 Poland 和烏克欄 Ukraine的歐洲國家盃2012的賽事和入球資料。

第一個例子列出球員姓氏為'Bender'的入球數據。 * 表示列出表格的全部欄位,簡化了寫matchid, teamid, player, gtime語句。

修改此SQL以列出 賽事編號matchid 和球員名 player ,該球員代表德國隊Germany入球的。要找出德國隊球員,要檢查: teamid = 'GER'

SELECT * FROM goal 
  WHERE player LIKE '%Bender'
SELECT matchid, player 
 FROM goal
   WHERE teamid LIKE 'GER'

由以上查詢,你可見Lars Bender's 於賽事 1012入球。.現在我們想知道此賽事的對賽隊伍是哪一隊。

留意在 goal 表格中的欄位 matchid ,是對應表格game的欄位id。我們可以在表格 game中找出賽事1012的資料。

只顯示賽事1012的 id, stadium, team1, team2

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

我們可以利用JOIN來同時進行以上兩個步驟。

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

語句FROM 表示合拼兩個表格game 和 goal的數據。語句 ON 表示如何找出 game中每一列應該配對goal中的哪一列 -- goalid 必須配對gamematchid 。 簡單來說,就是
ON (game.id=goal.matchid)

以下SQL列出每個入球的球員(來自goal表格)和場館名(來自game表格)

修改它來顯示每一個德國入球的球員名,隊伍名,場館和日期。

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

使用上題相同的 JOIN語句,

列出球員名字叫Mario (player LIKE 'Mario%')有入球的 隊伍1 team1, 隊伍2 team2 和 球員名 player

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

表格eteam 貯存了每一國家隊的資料,包括教練。你可以使用語句 goal JOIN eteam on teamid=id來合拼 JOIN 表格goal 到 表格eteam

列出每場球賽中首10分鐘gtime<=10有入球的球員 player, 隊伍teamid, 教練coach, 入球時間gtime

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

要合拼JOIN 表格game 和表格 eteam,你可以使用
game JOIN eteam ON (team1=eteam.id)

game JOIN eteam ON (team2=eteam.id)

注意欄位id同時是表格game 和表格 eteam的欄位,你要清楚指出eteam.id而不是只用id

列出'Fernando Santos'作為隊伍1 team1 的教練的賽事日期,和隊伍名。

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

列出場館 'National Stadium, Warsaw'的入球球員。

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






更困難的題目

以下例子找出德國-希臘Germany-Greece 的八強賽事的入球

修改它,只列出全部賽事,射入德國龍門的球員名字。

找非德國球員的入球,德國可以在賽事中作team1 隊伍1(主)或team2隊伍2(客)。 你可以用teamid!='GER' 來防止列出德國球員。 你可以用DISTINCT來防止球員出現兩次以上。

SELECT player, gtime
  FROM game JOIN goal ON matchid = id 
    WHERE (team1='GER' AND team2='GRE')
SELECT DISTINCT player
  FROM game JOIN goal ON matchid = id 
 WHERE (team1 = 'GER' OR team2 = 'GER')
   AND teamid!='GER'
列出隊伍名稱 teamname 和該隊入球總數

你應該在SELECT語句中使用COUNT(*)和使用GROUP BY teamname

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


列出場館名和在該場館的入球數字。
SELECT stadium,COUNT(1)
  FROM goal JOIN game ON id=matchid
GROUP BY stadium
每一場波蘭'POL'有參與的賽事中,列出賽事編號 matchid, 日期date 和入球數字。
SELECT matchid,mdate, team1, team2,teamid
  FROM game JOIN goal ON matchid = id 
 WHERE (team1 = 'POL' OR team2 = 'POL')
SELECT matchid,mdate,COUNT(teamid)
  FROM game JOIN goal ON matchid = id 
 WHERE (team1 = 'POL' OR team2 = 'POL')
GROUP BY matchid,mdate
每一場德國'GER'有參與的賽事中,列出賽事編號 matchid, 日期date 和德國的入球數字。
SELECT matchid,mdate,COUNT(teamid)
  FROM game JOIN goal ON matchid = id 
 WHERE (teamid='GER')
GROUP BY matchid,mdate
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.
mdateteam1score1team2score2
1 July 2012ESP4ITA 0
10 June 2012ESP1ITA1
10 June 2012IRL1CRO3
...

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,
  CASE WHEN teamid=team1 THEN 1 ELSE 0 END score1
  FROM game JOIN goal ON matchid = id
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
Clear your results

Old JOIN Tutorial

The next tutorial about the Movie database involves some slightly more complicated joins.