Question

我有test_scores表，其中包含以下字段：

表架构：

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

示例数据：

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

这对于什么是好的SQL？（我正在使用MySQL。）

原始要求不包括行集中的列名称。我能够使用以下SQL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

但是在结果集中引入了col_name，我感到难过......

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.

Answer 2

对于col_value，您需要使用GREATEST()。

至于col_name，你可以这样做，但它不是很优雅：

SELECT id,
       IF(score1 = col_value, 'score1',
       IF(score2 = col_value, 'score2',
       IF(score3 = col_value, 'score3', 'score4'))) AS col_name,
       col_value
FROM (
    SELECT *, 
           GREATEST(score1, score2, score3, score4) AS col_value
    FROM test_scores
) AS helper

Answer 3

解决方案的一部分（col_value）可以是SQL MAX of multiple columns?。

Answer 4

我更喜欢使用case语句的可读性，但我认为我只是为了踢而发布这个。

select GREATEST(score1, score2, score3, score4)
     , ELT(FIELD(GREATEST(score1, score2, score3, score4), score1, score2, score3, score4), 'score1', 'score2', 'score3', 'score4')
from (
    select 11 score1, 6 score2, 7 score3, 8 score4
) t

连续4列中的最大值

4 个答案: