Group Concat without conditionals - mysql

Question

I'm trying to rewrite my query to use columns instead of rows. I have this query:
mysql> SELECT r.id as responseId, a.id as answerId, o.id, optionId, q.label as questionLabel, o.label as optionLabel
-> FROM answer a
-> INNER JOIN question q ON questionId = q.id
-> INNER JOIN answer_options_option ao ON a.id = ao.answerId
-> INNER JOIN `option` o ON ao.optionId = o.id
-> INNER JOIN response r ON a.responseId = r.id
-> ORDER BY r.id, a.id, o.id;
Which gives me this output:
+------------+----------+----+----------+---------------+-------------+
| responseId | answerId | id | optionId | questionLabel | optionLabel |
+------------+----------+----+----------+---------------+-------------+
| 1 | 1 | 2 | 2 | Q1 | no |
| 1 | 2 | 4 | 4 | Q2 | b |
| 2 | 3 | 1 | 1 | Q1 | yes |
| 2 | 4 | 3 | 3 | Q2 | a |
| 2 | 4 | 4 | 4 | Q2 | b |
| 2 | 4 | 5 | 5 | Q2 | c |
+------------+----------+----+----------+---------------+-------------+
But I would like to get this output:
+------------+-----------+-------+
| responseId | Q1 | Q2 |
+------------+-----------+-------+
| 1 | no | b |
| 2 | yes | a,b,c |
+------------+-----------+-------+
So I threw together this query:
mysql> SELECT r.id as responseId,
-> IF(q.label = 'Q1', GROUP_CONCAT(o.label), NULL) as Q1,
-> IF(q.label = 'Q2', GROUP_CONCAT(o.label), NULL) as Q2
-> FROM answer a
-> INNER JOIN question q ON questionId = q.id
-> INNER JOIN answer_options_option ao ON a.id = ao.answerId
-> INNER JOIN `option` o ON ao.optionId = o.id
-> INNER JOIN response r ON a.responseId = r.id
-> GROUP BY r.id;
But it gives me this output instead:
+------------+-----------+------+
| responseId | Q1 | Q2 |
+------------+-----------+------+
| 1 | no,b | NULL |
| 2 | yes,a,b,c | NULL |
+------------+-----------+------+
Is it even possible to use GROUP_CONCAT like this? Is there another way to accomplish what I'm trying to do?
Here's a Fiddle.

Answer 1

You need to move the GROUP_CONCAT outside the conditional so that you aggregate the options based on the question instead of just getting the entire aggregated result based on the question value:
SELECT r.id as responseId,
GROUP_CONCAT(CASE WHEN q.label = 'Q1' THEN o.label END ORDER BY o.label) as Q1,
GROUP_CONCAT(CASE WHEN q.label = 'Q2' THEN o.label END ORDER BY o.label) as Q2
FROM answer a
INNER JOIN question q ON questionId = q.id
INNER JOIN answer_options_option ao ON a.id = ao.answerId
INNER JOIN `option` o ON ao.optionId = o.id
INNER JOIN response r ON a.responseId = r.id
GROUP BY r.id;
Output:
responseId Q1 Q2
1 no b
2 yes a,b,c
Demo on dbfiddle