MySQL查询以获取列和同一列的AVG之差

Question

I have a table which contains the scores by user, for a game:

UserID (Integer)
MatchId (Integer)
Score (Double)

I'd like to getter sum each user's "points above average" (PAA) - the amount by which a user's score was above or below the average.

So you'd need to calculate the average of 'Score' for each 'MatchId', then for each row in the table calculate the amount by which the 'Score' differs from the match average. And then sum that PAA value by user.

Is it possible to do this via a MySQL query? Or do I need PHP? If it can be done by query, what would that query look like?

Answer 1

plan

• compute avg scores by match
• join user scores to avg scores and compute sum of derived difference field by userid

---

setup

create table scores
(
  UserID integer not null,
  MatchId integer not null,
  Score decimal(5, 2) not null,
  primary key ( UserID, MatchId )
);

insert into scores
( UserID, MatchId, Score )
values
( 1, 1, 22.1 ),
( 2, 1, 36.0 ),
( 3, 1, 35.3 ),
( 1, 2, 50.0 ),
( 2, 2, 39.8 ),
( 3, 2, 42.0 )
;

query

select s.UserID, sum(s.Score - avgs.avg_score) as paa
from scores s
inner join
(
select MatchId, avg(Score) as avg_score
from scores
group by MatchId
) avgs
on s.MatchId = avgs.MatchId
group by s.UserID
;

output

+--------+-----------+
| UserID |    paa    |
+--------+-----------+
|      1 | -2.966666 |
|      2 | 0.733334  |
|      3 | 2.233334  |
+--------+-----------+

sqlfiddle