MySQL CASE WHEN numb IS NULL 忽略记录 WHERE numb IS NOT NULL

Question

我的表中有这些数据:

numb    m   value
8070    1   7.63
NULL    1   7.64
NULL    1   7.65
8070    2   7.939
8070    2   7.935
8070    2   7.941
NULL    3   7.62
8070    4   7.92
8070    4   7.935

对于每个m，我需要MIN(value)和MAX(value)，并且如果有一个值 code> 没有 numb (NULL)，那么那些有 numb 的应该被忽略。

所以我应该得到以下结果:

numb    m   value
NULL    1   7.64
NULL    1   7.65
8070    2   7.935
8070    2   7.941
NULL    3   7.62
8070    4   7.92
8070    4   7.935

我尝试了很多不同的方法，但似乎没有任何效果，而且我不知道如何查找相关信息。你能指出我正确的方向吗？

更新: 要获取值的数量，如下所示:

COALESCE(
IF(
  COUNT(
    CASE
      WHEN m IN (2, 4)
      THEN value
      ELSE
      CASE
        WHEN m IN (1, 3) AND numb IS NULL
        THEN value
      END
    END
  ) = 0,
  NULL,
  COUNT(
    CASE
      WHEN m IN (2, 4)
      THEN value
      ELSE
      CASE
        WHEN m IN (1, 3) AND numb IS NULL
        THEN value
      END
    END
  )
),
COUNT(
  CASE
    WHEN m IN (1, 3)
    AND numb IS NOT NULL
    THEN value
  END
)
) AS cnt

Answer 1

这个查询应该会给你你想要的结果。它有两层嵌套派生表。第一个:

SELECT m,
       MIN(CASE WHEN numb IS NULL THEN value END) AS min_null,
       MAX(CASE WHEN numb IS NULL THEN value END) AS max_null,
       MIN(CASE WHEN numb IS NOT NULL THEN value END) AS min_normal,
       MAX(CASE WHEN numb IS NOT NULL THEN value END) AS max_normal
FROM numbers
GROUP BY m;

计算每个m值的最小值和最大值，具体取决于numb是数字还是NULL。在下一个级别，

SELECT m,
       COALESCE(min_null, min_normal) AS min_value,
       COALESCE(max_null, max_normal) AS max_value
FROM (... query 1...)

我们使用计算要使用的适当的最小值和最大值(如果有 NULL 值，我们使用该值，否则我们使用与 numb 数值关联的值>)。最后，我们将数字表JOIN到查询2的结果，为每个m值找到适当的numb值:

SELECT n.numb, n.m, n.value
FROM numbers n
JOIN (... query 2 ...) num ON num.m = n.m AND (num.min_value = n.value OR num.max_value = n.value)
ORDER BY n.m, n.value

输出:

numb    m   value
null    1   7.64
null    1   7.65
8070    2   7.935
8070    2   7.941
null    3   7.62
8070    4   7.92
8070    4   7.935

Demo on dbfiddle

完整查询:

SELECT n.numb, n.m, n.value
FROM numbers n
JOIN (SELECT m,
             COALESCE(min_null, min_normal) AS min_value,
             COALESCE(max_null, max_normal) AS max_value
      FROM (SELECT m,
                   MIN(CASE WHEN numb IS NULL THEN value END) AS min_null,
                   MAX(CASE WHEN numb IS NULL THEN value END) AS max_null,
                   MIN(CASE WHEN numb IS NOT NULL THEN value END) AS min_normal,
                   MAX(CASE WHEN numb IS NOT NULL THEN value END) AS max_normal
            FROM numbers
            GROUP BY m) n) num ON num.m = n.m AND (num.min_value = n.value OR num.max_value = n.value)
ORDER BY n.m, n.value