sqlzoo练习答案--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

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 id from goal must match matchid fromgame. (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.

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

SELECT player,goal.teamid,stadium,mdate
  FROM game JOIN goal ON goal.matchid=game.id and goal.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 goal.matchid=game.id and goal.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 inner join eteam on eteam.id=goal.teamid
 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 eteamyou must specify eteam.id instead of just id

List the the dates of the matches and the name of the team in which ‘Fernando Santos‘ was the team1 coach.

SELECT game.mdate,eteam.teamname FROM game inner join eteam on eteam.id=game.team1 and eteam.coach=‘Fernando Santos‘

7、List the player for every goal scored in a game where the stadium was ‘National Stadium, Warsaw‘

select player from goal inner join game on game.id = goal.matchid and stadium=‘National Stadium, Warsaw‘

8、

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

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 goal inner join game on game.id = goal.matchid and goal.teamid!=‘GER‘ and (game.team1=‘GER‘ or game.team2=‘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(teamid) FROM eteam inner join goal on goal.teamid=eteam.id group by teamname

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

SELECT stadium,count(1) FROM game inner join goal on goal.matchid=game.id group by stadium

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

SELECT matchid,mdate,count(teamid) 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 inner join goal on game.id=goal.matchid and 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)
    score1,
    team2,
    SUM(CASE
    WHEN teamid=team2 THEN 1
    ELSE 0 END)
    score2
    FROM game left JOIN goal ON matchid = id group by mdate, matchid, team1,team2