title: Mysql subquery field unknown
body: <p>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)
  <a href="https://i.stack.imgur.com/wTBQQ.png" rel="nofollow noreferrer">The Query result</a></p>
  
  <pre><code>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;
  </code></pre>
  
  <p>However, I want only 2 records which contain the min and the max score values.</p>