Sql 两个情形函数之和

我试图对我刚刚在查询中创建的两个CASE函数求和。我需要这两列在我的结果集中返回，但也需要这两列的总和在另一列中返回为“DegreeDays”。我尝试了sum函数，但没有效果，我尝试了一个简单的“HeatingDegreeDays+CoolingDegreeDays as DegreeDays”，但也不起作用。建议

  ,CASE
    WHEN TempLow > 60.5                     THEN 0
    WHEN ((TempHigh + TempLow)/2) > 60.5    THEN ((60.5-TempLow)/4)
    WHEN  TempHigh >= 60.5                  THEN (((60.5 - TempLow)/2)-((TempHigh-TempLow)/4))
    WHEN TempHigh < 60.5                    THEN (60.5-(TempHigh+TempLow)/4)
   END AS HeatingDegreeDays

  ,CASE
    WHEN TempHigh < 66.25                   THEN 0
    WHEN ((TempHigh + TempLow)/2) < 66.25   THEN ((TempHigh-66.25)/4)
    WHEN  TempLow <= 66.25                  THEN (((TempHigh - 66.25)/2)-((66.25-TempLow)/4))
    WHEN TempLow > 66.25                    THEN ((TempHigh+TempLow)/2)-66.25
   END AS CoolingDegreeDays

---

您可以重复以下公式：

  ,CASE
    WHEN TempLow > 60.5                     THEN 0
    WHEN ((TempHigh + TempLow)/2) > 60.5    THEN ((60.5-TempLow)/4)
    WHEN  TempHigh >= 60.5                  THEN (((60.5 - TempLow)/2)-((TempHigh-TempLow)/4))
    WHEN TempHigh < 60.5                    THEN (60.5-(TempHigh+TempLow)/4)
   END +
   CASE
    WHEN TempHigh < 66.25                   THEN 0
    WHEN ((TempHigh + TempLow)/2) < 66.25   THEN ((TempHigh-66.25)/4)
    WHEN  TempLow <= 66.25                  THEN (((TempHigh - 66.25)/2)-((66.25-TempLow)/4))
    WHEN TempLow > 66.25                    THEN ((TempHigh+TempLow)/2)-66.25
   END AS TotalDays

---

一种方法是将现有查询简化为：

如果您使用的是SQL Server 2005或更高版本，这也将与以下功能一样有效：

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与仅仅为了计算而重复查询的逻辑和硬编码值相比，维护这两个选项中的任何一个似乎都更好。

当您在查询的“选择”部分中派生列名时，您不能在其他部分中引用它们

您有两个基本选项：

将DegreeDays定义为重复所有逻辑或执行以下操作的两个案例语句的总和：

select ...,HeatingDegreeDays,CoolingDegreeDays,DegreeDays=HeatingDegreeDays+CoolingDegreeDays
from table
cross apply (select
CASE
    WHEN TempLow > 60.5                     THEN 0
    WHEN ((TempHigh + TempLow)/2) > 60.5    THEN ((60.5-TempLow)/4)
    WHEN  TempHigh >= 60.5                  THEN (((60.5 - TempLow)/2)-((TempHigh-TempLow)/4))
    WHEN TempHigh < 60.5                    THEN (60.5-(TempHigh+TempLow)/4)
   END AS HeatingDegreeDays

  ,CASE
    WHEN TempHigh < 66.25                   THEN 0
    WHEN ((TempHigh + TempLow)/2) < 66.25   THEN ((TempHigh-66.25)/4)
    WHEN  TempLow <= 66.25                  THEN (((TempHigh - 66.25)/2)-((66.25-TempLow)/4))
    WHEN TempLow > 66.25                    THEN ((TempHigh+TempLow)/2)-66.25
   END AS CoolingDegreeDays
) x

---

非常感谢。真的很感激。我之前试过，但我一定是把语法搞砸了。我必须说，我认为复制代码的建议不是一个好的做法，特别是当你在回答的后半部分提到了一些简单而优雅的替代方案时。这样做对性能有好处吗？@TimLehner。这两种解决方案在SQL Server中的性能应该非常相似。一些数据库，尤其是MySQL，可能会实现子查询，这可能会对性能产生很大的负面影响。啊，真不幸！戈登，谢谢你再上一课。

SELECT a.HeatingDegreeDays,
    a.CoolingDegreeDays,
    a.HeatingDegreeDays + a.CoolingDegreeDays as DegreeDays
FROM
(
    SELECT
      CASE
        WHEN TempLow > 60.5                     THEN 0
        WHEN ((TempHigh + TempLow)/2) > 60.5    THEN ((60.5-TempLow)/4)
        WHEN  TempHigh >= 60.5                  THEN (((60.5 - TempLow)/2)-((TempHigh-TempLow)/4))
        WHEN TempHigh < 60.5                    THEN (60.5-(TempHigh+TempLow)/4)
       END AS HeatingDegreeDays

      ,CASE
        WHEN TempHigh < 66.25                   THEN 0
        WHEN ((TempHigh + TempLow)/2) < 66.25   THEN ((TempHigh-66.25)/4)
        WHEN  TempLow <= 66.25                  THEN (((TempHigh - 66.25)/2)-((66.25-TempLow)/4))
        WHEN TempLow > 66.25                    THEN ((TempHigh+TempLow)/2)-66.25
       END AS CoolingDegreeDays
    FROM MyTable
) AS a; -- Derived tabled aliased as "a"

;WITH cte AS (
    SELECT
      CASE
        WHEN TempLow > 60.5                     THEN 0
        WHEN ((TempHigh + TempLow)/2) > 60.5    THEN ((60.5-TempLow)/4)
        WHEN  TempHigh >= 60.5                  THEN (((60.5 - TempLow)/2)-((TempHigh-TempLow)/4))
        WHEN TempHigh < 60.5                    THEN (60.5-(TempHigh+TempLow)/4)
       END AS HeatingDegreeDays

      ,CASE
        WHEN TempHigh < 66.25                   THEN 0
        WHEN ((TempHigh + TempLow)/2) < 66.25   THEN ((TempHigh-66.25)/4)
        WHEN  TempLow <= 66.25                  THEN (((TempHigh - 66.25)/2)-((66.25-TempLow)/4))
        WHEN TempLow > 66.25                    THEN ((TempHigh+TempLow)/2)-66.25
       END AS CoolingDegreeDays
    FROM MyTable
)
SELECT HeatingDegreeDays,
    CoolingDegreeDays,
    HeatingDegreeDays + CoolingDegreeDays as DegreeDays
FROM cte;

select ...,HeatingDegreeDays,CoolingDegreeDays,DegreeDays=HeatingDegreeDays+CoolingDegreeDays
from table
cross apply (select
CASE
    WHEN TempLow > 60.5                     THEN 0
    WHEN ((TempHigh + TempLow)/2) > 60.5    THEN ((60.5-TempLow)/4)
    WHEN  TempHigh >= 60.5                  THEN (((60.5 - TempLow)/2)-((TempHigh-TempLow)/4))
    WHEN TempHigh < 60.5                    THEN (60.5-(TempHigh+TempLow)/4)
   END AS HeatingDegreeDays

  ,CASE
    WHEN TempHigh < 66.25                   THEN 0
    WHEN ((TempHigh + TempLow)/2) < 66.25   THEN ((TempHigh-66.25)/4)
    WHEN  TempLow <= 66.25                  THEN (((TempHigh - 66.25)/2)-((66.25-TempLow)/4))
    WHEN TempLow > 66.25                    THEN ((TempHigh+TempLow)/2)-66.25
   END AS CoolingDegreeDays
) x

,CASE
    WHEN TempLow > 60.5                     THEN 0
    WHEN ((TempHigh + TempLow)/2) > 60.5    THEN ((60.5-TempLow)/4)
    WHEN  TempHigh >= 60.5                  THEN (((60.5 - TempLow)/2)-((TempHigh-TempLow)/4))
    WHEN TempHigh < 60.5                    THEN (60.5-(TempHigh+TempLow)/4)
   END AS HeatingDegreeDays

  ,CASE
    WHEN TempHigh < 66.25                   THEN 0
    WHEN ((TempHigh + TempLow)/2) < 66.25   THEN ((TempHigh-66.25)/4)
    WHEN  TempLow <= 66.25                  THEN (((TempHigh - 66.25)/2)-((66.25-TempLow)/4))
    WHEN TempLow > 66.25                    THEN ((TempHigh+TempLow)/2)-66.25
   END AS CoolingDegreeDays