Difference between revisions of "The JOIN operation"

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This example shows all the games played in Warsaw.
 
This example shows all the games played in Warsaw.
  
<p class='imper'>Show '''date''', '''team1''' and '''team2''' for all matches of Polish ('POL') and Czech ('CZE') teams.</p>
+
<p class='imper'>Show '''date''', '''team1''' and '''team2''' for all matches that Polish ('POL') and Czech ('CZE') teams played in Warsaw.</p>
  
 
<source lang='sql' class='def'>
 
<source lang='sql' class='def'>

Revision as of 13:44, 2 August 2012

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.

Summary

The first example shows the goal scored by 'Wayne Rooney'.

Show matchid and player name for all goals scored by English players. teamid = 'ENG'

SELECT * FROM goal 
  WHERE player LIKE '%Rooney'
SELECT matchid, player 
 FROM game JOIN goal ON matchid = id
   WHERE teamid LIKE 'ENG'

This example shows all the games played in Warsaw.

Show date, team1 and team2 for all matches that Polish ('POL') and Czech ('CZE') teams played in Warsaw.

SELECT mdate, team1, team2 FROM game 
  WHERE stadium = 'National Stadium, Warsaw'
SELECT mdate, team1, team2 FROM game 
  WHERE stadium = 'National Stadium, Warsaw' 
    AND (team1 = 'POL' OR team1 = 'CZE')


More difficult questions

This query shows all goals scored in Germany-Greece quarterfinal.

Show names of all non-German players who scored a goal in matches against Germany.

Select goals scored by non-German players in matches where GER was the id of either team1 or team2.
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.

Show team1, team2 and results of all matches played at 'PGE Arena Gdansk' stadium.
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.

Show id of matches in which team1 scored at least two more goals than team2.
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.

Show players that scored a goal at 'National Stadium, Warsaw' in a day (mdate) when Czech Republic ('CZE') didn't play a match. Use 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.

Show teamid and count of goals for all 8 teams that have played more than 3 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)
Clear your results

JOIN Quiz Old JOIN Tutorial

The next tutorial about the Movie database involves some slightly more complicated joins.

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