Difference between revisions of "The JOIN operation"
m (Q2: "for game 1012" in question, "WHERE id=1023")
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Revision as of 12:31, 1 October 2012
|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|
|CZE||Czech Republic||Michal Bilek|
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.
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=1012
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.
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
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
Show names of all players who scored a goal against Germany.
Select goals scored by non-German players in matches where GER was the id of either team1 or team2.
You can use
teamid!='GER' to prevent listing German players.
You can use DISTINCT to stop players being listed twice.
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'
You should COUNT(*) in the SELECT line and 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
SELECT stadium,COUNT(1) FROM goal JOIN game ON id=matchid GROUP BY stadium
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
SELECT matchid,mdate,COUNT(teamid) FROM game JOIN goal ON matchid = id WHERE (teamid='GER') GROUP BY matchid,mdate
|1 July 2012||ESP||4||ITA||0|
|10 June 2012||ESP||1||ITA||1|
|10 June 2012||IRL||1||CRO||3|
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.
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 JOIN goal ON matchid = id GROUP BY mdate,matchid,team1,team2