SQLZOO:The JOIN operation

1.The first example shows the goal scored by a player with the last name ‘Bender’. The * says to list all the columns in the table - a shorter way of saying matchid, teamid, player, gtime

SELECT * FROM goal
WHERE player LIKE ‘%Bender’

Modify it to show the matchid and player name for all goals scored by Germany. To identify German players, check for: teamid = ‘GER’

SELECT matchid,player 
FROM goal 
WHERE teamid = 'GER'

2.From the previous query you can see that Lars Bender’s scored a goal in game 1012. Now we want to know what teams were playing in that match.

Notice in the that the column matchid in the goal table corresponds to the id column in the game table. We can look up information about game 1012 by finding that row in the game table.

Show id, stadium, team1, team2 for just game 1012

SELECT id,stadium,team1,team2
FROM game
where id=1012;

3.You can combine the two steps into a single query with a JOIN.

SELECT *
FROM game JOIN goal ON (id=matchid)

The FROM clause says to merge data from the goal table with that from the game table. The ON says how to figure out which rows in game go with which rows in goal - the matchid from goal must match id from game. (If we wanted to be more clear/specific we could say

ON (game.id=goal.matchid)

The code below shows the player (from the goal) and stadium name (from the game table) for every goal scored.

SELECT player,stadium
FROM game JOIN goal ON (id=matchid)

Modify it to show the player, teamid, stadium and mdate for every German goal.

SELECT player,teamid,stadium,mdate
FROM game JOIN goal ON (id=matchid)
where teamid='ger';

4.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%';

5.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,coach,gtime
FROM goal join eteam on teamid=id
WHERE gtime<=10;

6.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 and the name of the team in which ‘Fernando Santos’ was the team1 coach.

select mdate,teamname
from game join eteam on team1=eteam.id
where coach like 'Fernando Santos';

• 虽然题目中说也可以用 team2=eteam.id 来组合两个表格，但按题目要求，如果把代码换成team2=eteam.id会得到错误结果。
  7.List the player for every goal scored in a game where the stadium was ‘National Stadium, Warsaw’

select player
from goal join game on matchid=id
where stadium='National Stadium, Warsaw';

8.The example query shows all goals scored in the Germany-Greece quarterfinal.

SELECT player, gtime
FROM game JOIN goal ON matchid = id
WHERE (team1=‘GER’ AND team2=‘GRE’)

Instead show the name of all players who scored a goal against Germany.

HINT
Select goals scored only 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 distinct player
FROM game JOIN goal ON matchid = id 
WHERE ((team1!='GER' and team2='GER') 
or (team2!='GER' and team1='GER'))
and teamid!='ger';

9.Show teamname and the total number of goals scored.
COUNT and GROUP BY
You should COUNT(*) in the SELECT line and GROUP BY teamname

SELECT teamname,count(teamname)
FROM eteam JOIN goal ON id=teamid
group BY teamname;

10.Show the stadium and the number of goals scored in each stadium.

select stadium,count(stadium)
from game join goal on id=matchid
group by stadium;

11.For every match involving ‘POL’, show the matchid, date and the number of goals scored.

SELECT matchid,mdate,count(matchid)
FROM game JOIN goal ON matchid = id 
WHERE (team1 = 'POL' OR team2 = 'POL')
group by matchid;

12.For every match where ‘GER’ scored, show matchid, match date and the number of goals scored by ‘GER’

select matchid,mdate,count(teamid)
from game join goal on id=matchid
where teamid='ger'
group by matchid;

13.List every match with the goals scored by each team as shown. This will use “CASE WHEN” which has not been
explained in any previous exercises.
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. Sort your result by mdate, matchid, team1 and team2.

SELECT mdate,team1,
sum(CASE WHEN teamid=team1 THEN 1 ELSE 0 END) as score1,
team2,
sum(case when teamid=team2 then 1 else 0 end) as score2
FROM game left JOIN goal ON matchid = id 
group by mdate, matchid, team1,team2;