The JOIN operation

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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
1001 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
...


JOIN and UEFA EURO 2012

This tutorial introduces JOIN which allows you to use data from two or more tables. The tables contain all matches and goals from UEFA EURO 2012 Football Championship in Poland and Ukraine.

Summary

The first example shows the goal scored by 'Bender'.

Show matchid and player name for all goals scored by Germany. teamid = 'GER'

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

From the previous query you can see that Lars Bender's goal was scored in game 1012. Notice that the column matchid in the goal table corresponds to the id column in the game table.

Show id, stadium, team1, team2 for game 1012

SELECT id,stadium,team1,team2
  FROM game 
 WHERE stadium LIKE '%Warsaw%'
SELECT id,stadium,team1,team2
 FROM game
WHERE id=1023

You can combine the two steps into a single query with a join. You will get all the game details and all the goal details if you use

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

Show the player, teamid and mdate and for every German goal. teamid='GER'

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

Use the same join as in the previous question.

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%'

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

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

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

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

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

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

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

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






More difficult questions

This query shows all goals scored in Germany-Greece quarterfinal.

Show names of all non-German players who scored a goal in matches against Germany.

Select goals scored by non-German players in matches where GER was the id of either team1 or team2.
SELECT player, gtime
  FROM game JOIN goal ON matchid = id 
    WHERE (team1 = "GER" AND team2 = "GRE")
SELECT player 
  FROM game JOIN goal ON matchid = id 
    WHERE (team1 = "GER" OR team2 = "GER") 
    AND teamid != "GER"

The example shows result of the final match. COUNT() has been used to count the total number of goals.

Show team1, team2 and results of all matches played at 'PGE Arena Gdansk' stadium.
SELECT team1, team2, 
   (SELECT COUNT(*) FROM goal 
     WHERE matchid = id AND teamid = team1) 
   AS team1, 
   (SELECT COUNT(*) FROM goal 
     WHERE matchid = id AND teamid = team2) 
   AS team2 
  FROM game WHERE id = 1031
SELECT team1, team2, 
   (SELECT COUNT(*) FROM goal 
     WHERE matchid = id AND teamid = team1) 
   AS team1, 
   (SELECT COUNT(*) FROM goal 
     WHERE matchid = id AND teamid = team2) 
   AS team2 
  FROM game WHERE stadium = 'PGE Arena Gdansk'


The following query shows matches which were won by team1.

Show id of matches in which team1 scored at least two more goals than team2.
SELECT team1, team2 FROM game WHERE 
   (SELECT COUNT(*) FROM goal 
     WHERE matchid = id AND teamid = team1) >
   (SELECT COUNT(*) FROM goal 
     WHERE matchid = id AND teamid = team2)
SELECT id FROM game WHERE 
   (SELECT COUNT(*) FROM goal 
     WHERE matchid = id AND teamid = team1) -
   (SELECT COUNT(*) FROM goal 
     WHERE matchid = id AND teamid = team2) >= 2

The example shows teams that scored a goal at stadiums where Poland has played its matches.

Show players that scored a goal at 'National Stadium, Warsaw' in a day (mdate) when Czech Republic ('CZE') didn't play a match. Use DISTINCT to remove duplicates from your query results.
SELECT DISTINCT teamid 
  FROM game JOIN goal ON matchid = id 
    WHERE Stadium IN 
        (SELECT stadium FROM game 
           WHERE team1 = 'POL' OR team2 = 'POL')
SELECT DISTINCT player 
  FROM game JOIN goal ON matchid = id 
    WHERE stadium = 'National Stadium, Warsaw'
      AND mdate NOT IN 
        (SELECT mdate FROM game 
           WHERE team1 = 'CZE' OR team2 = 'CZE')

The query shows the stadiums, where the teams who scored more than 8 goals played their matches.

Show teamid and count of goals for all 8 teams that have played more than 3 matches.
SELECT teamid, COUNT(*) FROM goal 
  WHERE 3 < 
    (SELECT COUNT(DISTINCT id) FROM game 
       WHERE team1 = teamid OR team2 = teamid) 
  GROUP BY teamid
SELECT DISTINCT stadium 
  FROM game WHERE team1 IN
    (SELECT teamid FROM goal 
       GROUP BY teamid HAVING COUNT(*) > 8)
Clear your results

Old JOIN Tutorial

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

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