Difference between revisions of "The JOIN operation"
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<div class='qu'> | <div class='qu'> | ||
The table '''eteam''' gives details of every national team including the coach. You can JOIN '''goal''' to '''eteam''' using the phrase <code>goal JOIN eteam on teamid=id</code> | The table '''eteam''' gives details of every national team including the coach. You can JOIN '''goal''' to '''eteam''' using the phrase <code>goal JOIN eteam on teamid=id</code> | ||
− | <p class='imper'>Show player, | + | <p class='imper'>Show player, teamid, coach, gtime for all goals scored in the first 10 minutes <code>gtime<=10</code></p> |
<source lang='sql' class='def'> | <source lang='sql' class='def'> | ||
− | SELECT player, teamid | + | SELECT player, teamid, gtime |
FROM goal | FROM goal | ||
WHERE gtime<=10 | WHERE gtime<=10 | ||
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<source lang='sql' class='ans'> | <source lang='sql' class='ans'> | ||
− | SELECT player, teamid, coach | + | SELECT player, teamid, coach, gtime |
FROM goal JOIN eteam ON (teamid=id) | FROM goal JOIN eteam ON (teamid=id) | ||
WHERE gtime<=10 | WHERE gtime<=10 | ||
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<div class='qu'> | <div class='qu'> | ||
− | + | To JOIN '''game''' with '''eteam''' you could use either <code>game JOIN eteam ON (team1=eteam.id)</code> or <code>game JOIN eteam ON (team2=eteam.id)</code> | |
− | + | Notice that because '''id''' is a column name in both '''game''' and '''eteam''' you must specify '''eteam.id''' instead of just '''id''' | |
+ | <p class='imper'>List the dates of the matches in which 'Fernando Santos' was the team1 coach.</p> | ||
<source lang='sql' class='def'> | <source lang='sql' class='def'> | ||
− | + | ||
− | |||
− | |||
− | |||
</source> | </source> | ||
<source lang='sql' class='ans'> | <source lang='sql' class='ans'> | ||
− | SELECT | + | SELECT mdate,teamname |
− | FROM eteam | + | FROM game JOIN eteam ON (team1=eteam.id) |
− | + | WHERE coach='Fernando Santos' | |
− | |||
</source> | </source> | ||
</div> | </div> |
Revision as of 13:31, 29 September 2012
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 |
... |
matchid | teamid | player | gtime | |
---|---|---|---|---|
1001 | POL | Robert Lewandowski | 17 | |
1001 | GRE | Dimitris Salpingidis | 51 | |
1002 | RUS | Alan Dzagoev | 15 | |
1001 | RUS | Roman Pavlyuchenko | 82 | |
... |
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.
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'
This example uses COUNT()
, GROUP BY
and SELECT within SELECT
to show teams that have scored more goals than England. Add JOIN
and...
Show stadium and count of goals for stadiums where the number of goals is larger than number of goals scored by Spanish players (teamid = 'ESP') during the entire championship.
SELECT teamid, COUNT(*)
FROM goal
GROUP BY teamid
HAVING COUNT(*) >
(SELECT COUNT(*)
FROM goal WHERE teamid = 'ENG')
SELECT stadium, COUNT(*)
FROM game JOIN goal ON matchid = id
GROUP BY stadium
HAVING COUNT(*) >=
(SELECT COUNT(*)
FROM goal WHERE teamid = 'ESP')
More difficult questions
Show names of all non-German players who scored a goal in matches against Germany.
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.
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.
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.
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.
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)
The next tutorial about the Movie database involves some slightly more complicated joins.