Difference between revisions of "The JOIN operation"
(A left join is needed when combining the game and goal tables or else scoreless draws which have no entries in the goal table will not be returned)
|Line 227:||Line 227:|
<p class='imper'>List the player for every goal scored in a game where the
<p class='imper'>List the player for every goal scored in a game where the was 'National Stadium, Warsaw'</p>
<source lang='sql' class='def'>
<source lang='sql' class='def'>
Revision as of 22:12, 21 January 2014
|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
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%'
eteam gives details of every national team including the coach. You can
eteam using the phrase
goal JOIN eteam on teamid=id
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
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
eteam you must specify
eteam.id instead of just
List the the dates of the matches and the name of the team 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 stadium 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. (The "correct result" maybe wrong, because Robin is from NED team and he is not able to play in the GER vs GRE semi-final game.)
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. 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