Difference between revisions of "The JOIN operation"
Line 128: | Line 128: | ||
The first example shows the goal scored by 'Wayne Rooney'. | The first example shows the goal scored by 'Wayne Rooney'. | ||
− | <p class='imper'>Show '''matchid''' and '''player''' name for all goals scored by | + | <p class='imper'>Show '''matchid''' and '''player''' name for all goals scored by Germany. |
− | <code>teamid = ' | + | <code>teamid = 'GER'</code></p> |
<source lang='sql' class='def'> | <source lang='sql' class='def'> | ||
SELECT * FROM goal | SELECT * FROM goal | ||
− | WHERE player LIKE '% | + | WHERE player LIKE '%Bender' |
</source> | </source> | ||
Line 139: | Line 139: | ||
SELECT matchid, player | SELECT matchid, player | ||
FROM goal | FROM goal | ||
− | WHERE teamid LIKE ' | + | WHERE teamid LIKE 'GER' |
</source> | </source> | ||
</div> | </div> | ||
<div class='qu'> | <div class='qu'> | ||
− | From the previous query you can see that | + | 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. | |
− | <p class='imper'>Show id, stadium, team1, team2 for game | + | <p class='imper'>Show id, stadium, team1, team2 for game 1012</p> |
<source lang='sql' class='def'> | <source lang='sql' class='def'> | ||
Line 163: | Line 163: | ||
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 | 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 (game.id=goal.matchid) | SELECT * FROM game JOIN goal ON (game.id=goal.matchid) | ||
− | <p class='imper'>Show the player and the stadium for every | + | <p class='imper'>Show the player and the stadium for every German goal. <code>teamid='GER'</code></p> |
<source lang='sql' class='def'> | <source lang='sql' class='def'> | ||
− | SELECT | + | SELECT * |
− | + | FROM game JOIN goal ON (game.id=goal.matchid) | |
− | |||
</source> | </source> | ||
<source lang='sql' class='ans'> | <source lang='sql' class='ans'> | ||
− | SELECT | + | SELECT * |
− | WHERE | + | FROM game JOIN goal ON (game.id=goal.matchid) |
+ | WHERE teamid='GER' | ||
</source> | </source> | ||
</div> | </div> |
Revision as of 23:44, 28 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 'Wayne Rooney'.
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 (game.id=goal.matchid)
Show the player and the stadium for every German goal. teamid='GER'
SELECT *
FROM game JOIN goal ON (game.id=goal.matchid)
SELECT *
FROM game JOIN goal ON (game.id=goal.matchid)
WHERE teamid='GER'
The following query shows coaches of teams that played on 9 June 2012. JOIN
has been used to make relation between two tables. Because of this we can select coach from eteam
table and mdate from game
table.
Show stadium and mdate of matches played by the team having 'Vicente del Bosque' as the coach.
SELECT coach, mdate FROM eteam JOIN game
ON (team1 = eteam.id OR team2 = eteam.id)
WHERE mdate = '9 June 2012'
SELECT stadium, mdate FROM eteam JOIN game
ON (team1 = eteam.id OR team2 = eteam.id)
WHERE coach= 'Vicente del Bosque'
This example is using JOIN to display all goals scored during the UEFA EURO 2012 final (it was the only match in July).
Show all goals scored in Germany - Greece match. Use team1 and team2 values to find the match.
SELECT player, gtime FROM goal
JOIN game ON id = matchid
WHERE mdate LIKE '%July%'
SELECT player, gtime FROM goal
JOIN game ON id = matchid
WHERE team1 = 'GER' AND team2 = 'GRE'
This query shows names of the teams that have scored less than 5 goals in the entire championship.
Show player names and count of goals for players who scored more than 2 goals.
SELECT teamname, COUNT(*)
FROM eteam JOIN goal ON teamid = id
GROUP BY teamname
HAVING COUNT(*) < 5
SELECT player, COUNT(*)
FROM eteam JOIN goal ON teamid = id
GROUP BY player
HAVING COUNT(*) > 2
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.