连续4列中的最大值

Question

我有test_scores以下字段的表：

表架构：

  id (number)
  score1  (number)
  score2  (number)
  score3  (number)
  score4  (number)

样本数据：

id score1 score2 score3 score4
1  10     05      30    50
2  05     15      10    00
3  25     10      05    15

预期结果集：

id col_name col_value
1  score4   50
2  score2   15
3  score1   25

对此有什么好的SQL？（我正在使用MySQL。）

原始要求未在行集中包含列名称。我可以使用以下SQL来获得结果：

SELECT   A.id, MAX(A.score) AS max_score
FROM     (
            SELECT id, score1 as score FROM test_scores UNION
            SELECT id, score2 as score FROM test_scores UNION
            SELECT id, score3 as score FROM test_scores UNION
            SELECT id, score4 as score FROM test_scores
          ) AS A
GROUP BY A.id

但是由于在结果集中引入了col_name，我感到很困惑。

Answer 1

我使用以下SQL解决了这个问题：

SELECT id, GREATEST(score1, score3, score3, score4) AS col_value,
       CASE GREATEST(score1, score3, score3, score4) 
         WHEN score1 THEN 'score1'
         WHEN score2 THEN 'score2'
         WHEN score3 THEN 'score3'
         WHEN score4 THEN 'score4'
       END AS col_name
FROM test_scores

Please let me know if there is a better solution.