sql 服务器中的最小函数无法正常工作，给出 0

Question

我想用今天的最小值减去今天的最大值。我正确地得到最大值，但最小值变为 0。如何从 kvarh 的最大值中减去今天的最小值。

数据类型 kvarh - float，devicetimestamp - datetime

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

示例数据

     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

Answer 1

我已经检查了你的查询，它工作正常。你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, 868996, '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 return 0 使用此示例数据 - 如果未找到任何行，您将得到 NULL 作为结果。只有只有一行符合你的条件时你才会得到0，因为你会减去相同的值

例如：

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, 868996, '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';

Answer 2

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

Answer 3

QuYour min 子查询可以有 0 >>WHERe DeviceTimeStamp < GETDATE()

   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

sql 服务器中的最小函数无法正常工作，给出 0

Min function in sql server is not working properly giving 0

tsql

sql-server

datetime

max

min