Question

I’m sure this sort of question has come up before but I’ve been searching and can’t find anything similar to what I need.

Edit: so after some reading this looks like it falls under pivots and uses group concat. If anybody has any insight id really appreciate it.

I have 3 tables (unnecessary fields & data stripped out for simplicity):

Students
id       name
------------------
1        John
2        Jane



Tests
id     name
------------------
1      Test1
2      Test2



Results
id    test_id     student_id   result
--------------------------------------
1     1           1            90
2     1           2            70
3     2           1            50
4     2           2            95

What I want is to be able to produce a table like this:

Name     Average    Test1    Test2
-----------------------------------
John     70         90        50
Jane     92.5       70        95

I know how to get the average, and I’m sure I could do this with an ugly set of loops and php logic but I’d like to get the most efficient solution. Any help is greatly appreciated.

Answer 1

SELECT
    s.name,
    avg(r.result) AS average,
    t1.result AS test1,
    t2.result AS test2
FROM
    students s,
    results r,
    results t1,
    results t2
WHERE
    r.student_id = s.id AND
    t1.test_id = 1 AND
    t1.student_id = s.id AND
    t2.test_id = 2 AND
    t2.student_id = s.id
GROUP BY s.id;

+------+---------+-------+-------+
| name | average | test1 | test2 |
+------+---------+-------+-------+
| John |      70 |    90 |    50 | 
| Jane |    82.5 |    70 |    95 | 
+------+---------+-------+-------+

Edit: You can’t really make the test columns dynamically based on the contents of the tests table. You can pick specific values to use as columns though.