Difference between revisions of "The JOIN operation"
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Notice that because <code>id</code> is a column name in both <code>game</code> and <code>eteam</code> you must specify <code>eteam.id</code> instead of just <code>id</code> | Notice that because <code>id</code> is a column name in both <code>game</code> and <code>eteam</code> you must specify <code>eteam.id</code> instead of just <code>id</code> | ||
− | <p class='imper'>List the dates of the matches in which 'Fernando Santos' was the team1 coach.</p> | + | <p class='imper'>List the name of the team and the dates of the matches in which 'Fernando Santos' was the team1 coach.</p> |
<source lang='sql' class='def'> | <source lang='sql' class='def'> |
Revision as of 22:20, 29 December 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=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. 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 name of the team and 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
mdate | team1 | score1 | team2 | score2 |
---|---|---|---|---|
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
The next tutorial about the Movie database involves some slightly more complicated joins.