SELECT a.test_id
     , b.name test_name
     , a.subject_id
     , c.subject_name
     , a.sum_score
     , d.level_name
  FROM (SELECT test_id
             , subject_id
             , SUM(score) sum_score
          FROM score
         GROUP BY test_id, subject_id
        ) a
 INNER JOIN test b
    ON a.test_id = b.test_id
 INNER JOIN subject c
    ON a.test_id = c.test_id
   AND a.subject_id = c.subject_id
  LEFT OUTER JOIN level d
    ON a.test_id = d.test_id
   AND a.sum_score >= d.sum_score
  LEFT OUTER JOIN level e
    ON d.test_id = e.test_id
   AND d.sum_score < e.sum_score
 WHERE e.sum_score IS NULL
;