SQL: Counting number of games for team from results page - sql

Question

Completely noob to SQL.
I have created the following table, which stores data on matches between two opponents and the points the winner got.
CREATE TABLE matches ( winner INT references players,
loser INT references players,
gamepoints INT);
I created the below VIEW to show standings:
CREATE VIEW standings as
select
players.id,
players.name,
count(matches.winner) as number_of_wins,
coalesce(sum(matches.gamepoints),0) as points
from players left join matches
on players.id = matches.winner
group by players.name, players.id
order by number_of_wins desc, points desc;
I wish to add a column that will show how many games a player played. My problem is that games appear in both matches.winner and matches.loser columns, and I'm not sure how to aggregate them in the standings view.
Also, would you say that the matches table is normalized?
Any help would be greatly appreciated.
EDIT: changed matches content.

Answer 1

With the help of #Jorge Campos, this is the solution:
CREATE VIEW games_won as
select p.id, p.name, coalesce(sum(m.gamepoints),0) gp, count(m.winner) ng
from players p left join matches m
on p.id=m.winner
group by p.id, p.name;
CREATE VIEW games_lost as
select p.id, p.name, count(m.loser) as ng
from players p left join matches m
on p.id=m.loser
group by p.id, p.name;
CREATE VIEW standings as
select w.id, w.name, w.ng as wins, w.ng+l.ng as matches, w.gp as gamepoints
from games_won w INNER JOIN games_lost l
on w.id=l.id
order by wins desc, gamepoints;

Answer 2

For the simple case you show there are only a few things that you should fix to be ok. Again for the problem you show.
First: Change the columns types of the table matches it shouldn't be SERIAL as it is an autoincrement type column (not a real type). Both columns are foreign keys and it should be integer, int or bigint
as
create table matches (
winner bigint,
loser bigint,
gamepoints int,
constraint fk_player_winner foreign key (winner)
references players(id),
constraint fk_player_loser foreign key (loser)
references players(id)
);
Second: to know how many games a player did with the number of points you can create two subqueries one with the winners and one with the losers and join the two summing the values. The catch is that you have to decrease the gamepoints from the two:
select w.id, w.name, w.gp-l.gp as gamepoints, w.ng+l.ng
from (select p.id, p.name, sum(m.gamepoints) gp, count(m.winner) as ng
from players p inner join matches m
on p.id=m.winner
group by p.id, p.name ) w
INNER JOIN
(select p.id, p.name, sum(m.gamepoints) gp, count(m.loser) as ng
from players p inner join matches m
on p.id=m.loser
group by p.id, p.name) l on w.id=l.id;
From it you create your view.
Note: maybe I'm being overkill with this two subqueries. It is possible to work out with a join between two players tables and a matches
See how it goes here on fiddle: http://sqlfiddle.com/#!15/5b6a4/4