Difference between revisions of "The JOIN operation"

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')

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.

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)