sqlzoo練習答案--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
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 innerjoin eteam on eteam.id=goal.teamid
- WHERE gtime<=10
6、
To JOIN
game
with eteam
you
could use eithergame 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 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 innerjoin 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 innerjoin game on game.id = goal.matchid and stadium='National Stadium, Warsaw'
Instead show the name of all players who scored a goal against Germany.
HINTSelect 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.
- selectDISTINCT(player) from goal innerjoin 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 innerjoin goal on goal.teamid=eteam.id groupby teamname
10、Show the stadium and the number of goals scored in each stadium.
- SELECT stadium,count(1) FROM game innerjoin goal on goal.matchid=game.id groupby 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') groupby 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 innerjoin goal on game.id=goal.matchid and teamid='GER'groupby 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.mdate | team1 | score1 | team2 | score2 |
---|---|---|---|---|
1 July 2012 | ESP | 4 | ITA | 0 |
10 June 2012 | ESP | 1 | ITA | 1 |
10 June 2012 | IRL | 1 | CRO | 3 |
... |
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 leftJOIN goal ON matchid = id groupby mdate, matchid, team1,team2