SQL Server中的最小功能无法正常工作给0

问题描述

我想从今天的最小值减去今天的最大值。我可以正确地获得最大值，但最小值却变为0。如何从kvarh的最大值中减去今天的最小值。

数据类型kvarh-浮点数，devicetimestamp-日期时间

代码

   select(
  SELECT MAX(kvarh)
  FROM [Transformer].[dbo].[Total_Power]
 WHERe DeviceTimeStamp < GETDATE()
 and DEVICEIMEI = '868996')
 -
  (SELECT MIN(kvarh)
  FROM [Transformer].[dbo].[Total_Power]
 WHERe DeviceTimeStamp < GETDATE()
 and DEVICEIMEI = '868996')
  as Difference

样本数据

     A_id   DeviceImei  DeviceTimeStamp           KWH       KVARH       
    985302  868996     2020-10-16 10:30:30.000  36682.5     424107.1    
    985298  868996     2020-10-16 10:15:31.000  36678.94    424103.3    
    985296  8689960    2020-10-16 10:00:29.000  36675.88    424099.8    

解决方法

我已经检查了您的查询，并且工作正常。您可以像这样减少一点：

DECLARE @DataSource TABLE
(
    [A_id] INT,[DeviceImei]  INT,[DeviceTimeStamp] DATETIME,[KWH] DECIMAL(9,2),[KVARH] DECIMAL(9,2)
);

INSERT INTO @DataSource ([A_id],[DeviceImei],[DeviceTimeStamp],[KWH],[KVARH])
VALUES (985302,868996,'2020-10-16 00:30:30.000',36682.5,424107.1),(985298,'2020-10-16 00:15:31.000',36678.94,424103.3),(985296,8689960,'2020-10-16 00:00:29.000',36675.88,424099.8);


SELECT MAX(kvarh) - MIN(kvarh) AS Difference
FROM @DataSource
WHERE DeviceTimeStamp < GETDATE()
   and DEVICEIMEI = '868996';

MIN函数不会将此示例数据返回0-如果未找到任何行，您将得到NULL的结果。仅当只有一行符合您的条件时，您才会获得0，因为您将减去相同的值。

例如：

DECLARE @DataSource TABLE
(
    [A_id] INT,424107.1)
      --,424099.8);


SELECT MAX(kvarh) - MIN(kvarh) AS Difference
FROM @DataSource
WHERE DeviceTimeStamp < GETDATE()
   and DEVICEIMEI = '868996';

,

select(
select max(KVARH) from [Transformer].[dbo].[Total_Power] 
where cast(DeviceTimeStamp as Date)  = cast(getdate() as Date) and DEVICEIMEI = '868996'
)
-
(
select min(KVARH) from [Transformer].[dbo].[Total_Power] 
where cast(DeviceTimeStamp as Date)  = cast(getdate() as Date) and DEVICEIMEI = '868996'
)
as Todays_Consumption

,

QuYour min子查询可能具有0 >> WHERE DeviceTimeStamp

   select(
  SELECT MAX(kvarh)
  FROM [Transformer].[dbo].[Total_Power]
  WHERe DeviceTimeStamp < GETDATE()
  and DEVICEIMEI = '868996')
  -
   (SELECT MIN(kvarh)  /*could have 0 value*/
   FROM [Transformer].[dbo].[Total_Power]
   WHERe DeviceTimeStamp < GETDATE()
   and DEVICEIMEI = '868996'
   and kvarh >0)/*try adding this*/
   as Difference