来自多个联接的SQL错误SUMS

Question

I'm trying to sum multiple tables using Joins and Sums in MySQL and not having much success.

My Tables (Unnecessary Columns Removed)

Students

idStudent   studentname   studentyear
1           foobar        11
2           barfoo        11
3           thing         8

Athletics_Results

idResult   idStudent   points
1          1           14
2          1           11
3          3           7
4          2           9

Team_Results

idTeamResults   year   points
1               11     9
2               8      8
3               7      14

So let me explain about the tables, because I admit they're poorly named and designed.

Students holds the basic info about each student, including their year and name. Each student has a unique ID.

Athletics_Results stores the results from athletics events. The idStudent column is a foreign key and relates to idStudent in the student column. So student foobar (idStudent 1) has scored 14 and 11 points in the example.

Team_Results stores results from events that more than one student took part in. It just stores the year group and points.

The Aim

I want to be able to produce a sum of points for each year - combined from both athletics_results and team_results. EG:

year   points
7      14     <-- No results in a_r, just 14 points in t_r
8      15     <-- 7 points in a_r (idResult 4) and 8 in t_r
11     43     <-- 14, 11, 9 points in a_r and 9 in t_r

What I've tried For testing purposes, I've not tried combining the a_r scores and t_r scores yet but left them as two columns so I can see what's going on.

The first query I tried:

SELECT students.studentyear as syear, SUM(athletics_results.points) as score, SUM(team_results.points) as team_score
FROM students
JOIN team_results ON students.studentyear = team_results.year
JOIN athletics_results ON students.idStudent = athletics_results.idStudent
GROUP BY syear;

This gave different rows for each year (as desired) but had incorrect SUMS. I learnt this was due to not grouping the joins.

I then created this code:

SELECT studentyear as sYear, teamPoints, AthleticsPoints
FROM students st

JOIN    (SELECT year, SUM(tm.points) as teamPoints
        FROM team_results tm
        GROUP BY year) tr ON st.studentyear = tr.year 

JOIN    (SELECT idStudent, SUM(atr.points) as AthleticsPoints
        FROM athletics_results atr
        ) ar ON st.idStudent = ar.idStudent

Which gave correct SUMS but only returned one year group row (eg the scores for Year 11).

EDIT - SQLFiddle here: http://sqlfiddle.com/#!9/dbc16/ . This is with my actual test data which is a bigger sample than the data I posted here.

Answer 1

http://sqlfiddle.com/#!9/ad111/7

SELECT tr.`year`,  COALESCE(tr.points,0)+COALESCE(SUM(ar.points),0)
FROM Team_Results tr
LEFT JOIN Students s
ON tr.`year`=s.studentyear
LEFT JOIN Athletics_Results ar
ON s.idStudent = ar.idStudent
GROUP BY tr.year

According to your comment and fiddle provided check http://sqlfiddle.com/#!9/dbc16/3

SELECT tr.`year`,  COALESCE(tr.points,0)+COALESCE(SUM(ar.points),0)
FROM (
  SELECT `year`, SUM(points) as points
  FROM Team_Results
  GROUP BY `year`) tr
LEFT JOIN Students s
ON tr.`year`=s.studentyear
LEFT JOIN Athletics_Results ar
ON s.idStudent = ar.idStudent
GROUP BY tr.year

Answer 2

Can be done in multiple ways. My first thought is:

SELECT idStudent, year, SUM(points) AS totalPoints FROM (
SELECT a.idStudent, c.year, a.points+b.points AS points
FROM students a
INNER JOIN Athletics_Results b ON a.idStudent=b.idStudent
INNER JOIN Team_Results c ON a.studentyear=c.year) d
GROUP BY idStudent,year

Answer 3

Try this http://sqlfiddle.com/#!9/2bfb1/1/0

SELECT 
    year, SUM(points)
FROM
    ((SELECT 
        a.year, SUM(b.points) AS points
    FROM
        student a
    JOIN at_result b ON b.student_id = a.id
    GROUP BY a.year) UNION (SELECT 
        a.year, SUM(a.points) AS points
    FROM
        t_result a
    GROUP BY a.year)) c
GROUP BY year;

On your data I get:

   year      points 
    7          14
    8          15
    11         43