Mysql subquery field unknown - mysql

Question

I have read many posts have a solution for this but this does not work in my case. What am I doing wrong?
- This gives me the SUM of scores for every user and this is the first part.( Aggregated Data)
The Query result
SELECT user_id, sum(score) as total_user_score
FROM (
SELECT comments_proper.user_id, comments_proper.score
FROM assignment_2.comments_proper
) AS rsch
GROUP BY user_id;
However, I want only 2 records which contain the min and the max score values.

Answer 1

What am I doing wrong?
Oh dear, where to begin.
I have read many posts
You should have been paying attention to which ones got up-voted and good answers, and which were down-voted/closed. The former would have included the table structures, examples of input and expected output. And unambiguous questions.
I want only 2 records
Is that from the source data set or from the aggregated data set?
The latter is a slightly tricky problem which has been asked and answered many times here on SO, there are multiple solutions with different performance characteristics. There's even a chapter in the manual covering just this question. The current content at that link uses subqueries to identify the min/max value which replaces an earlier version of the documentation which explained the max-concat trick, but its also possible to use variables to identify the right caddidate rows in a sub-query or to use sorting.
However the SQL you've shown us here, has very little to do with solving the problem you describe, and is very badly written.
I won't provide examples of every solution, but this will solve your problem...
SELECT user_id, SUM(score)
FROM assignment_2.comments_proper
GROUP BY user_id
ORDER BY SUM(score)
UNION
SELECT user_id, SUM(score)
FROM assignment_2.comments_proper
GROUP BY user_id
ORDER BY SUM(score)
updated
I hadn't tested the above. I did test this:
SELECT *
FROM (
SELECT user_id, SUM(score)
FROM assignment_2.comments_proper
GROUP BY user_id
ORDER BY SUM(score) LIMIT 0,1
) as lowest
UNION ALL
SELECT *
FROM (
SELECT user_id, SUM(score)
FROM assignment_2.comments_proper
GROUP BY user_id
ORDER BY SUM(score) DESC LIMIT 0,1
) as highest

Answer 2

In your queries you have some problem of sintax and a too complex calculation for aggregated resul anyway .. in cp1.* result you have the min related values in cp2.* the max related.
If you need all the resuly for min and max rows on the same row you can use a couple of inner join based on the aggregated result
select cp1.* , cp2.*
from ( SELECT cp.user_id, sum(cp.score), min(cp.score) min_score, max(cp.score) max_score
FROM assignment_2.comments_proper cp
group by cp.user_id ) t
inner join assignment_2.comments_proper cp1 on cp1.user_id = t.user_id
and cp1.score = t.min_score
inner join assignment_2.comments_proper cp2 on cp2.user_id = t.user_id
and cp2.score = t.max_score
otherwise if you want the result in two rows one for min and one for max
select 'min' , cp1.*
from ( SELECT cp.user_id, sum(cp.score), min(cp.score) min_score, max(cp.score) max_score
FROM assignment_2.comments_proper cp
group by cp.user_id ) t
inner join assignment_2.comments_proper cp1 on cp1.user_id = t.user_id
and cp1.score = t.min_score
union
select 'max' , cp2.*
from ( SELECT cp.user_id, sum(cp.score), min(cp.score) min_score, max(cp.score) max_score
FROM assignment_2.comments_proper cp
group by cp.user_id ) t
inner join assignment_2.comments_proper cp2 on cp2.user_id = t.user_id
and cp2.score = t.max_score