Question

我想从另一个值中减去一个值。该表的架构如下：

   tag, datetime,value
   ------------
   tag1, 2010-1-1 10:10:00, 123
   tag2, 2010-2-2 10:12:00. 321

  select * from  

  ( (Select    Max(Value) as [Value1] from History WHERE Datetime ='2010-1-1 10:10'       and tagname ='tag1') as v1   -

  (  (Select    Max(Value) as [Value2] from History WHERE Datetime ='2010-1-1 10:12'      and Tagname ='tag2')  as v2))

显然我迷路了...我该怎么做。

感谢

MS-SQL

Answer 1

总猜：

select v1.Value1 - v2.Value2 from  

  (Select    Max(Value) as [Value1] from History WHERE Datetime ='2010-1-1 10:10' and tagname ='tag1') as v1   

CROSS JOIN

  (  (Select    Max(Value) as [Value2] from History WHERE Datetime ='2010-1-1 10:12'      and Tagname ='tag2')  as v2)

Answer 2

你真的需要包装select语句吗？

您可以声明两个变量@value1和@value2并对其进行子结构化。

declare @value1 int, @value2 int

select @value1 = Max(Value) as [Value1] from History WHERE Datetime ='2010-1-1 10:10'       and tagname ='tag1'

select @value2 = Max(Value) as [Value2] from History WHERE Datetime ='2010-1-1 10:12'      and Tagname ='tag2'

select @value1 - @value2

Answer 3

值列的类型是什么？如果它已经是整数，那就做：

SELECT 

  (Select Max(Value) as [Value1] from History WHERE Datetime ='2010-1-1 10:10'       and tagname ='tag1') as v1   -

  (Select Max(Value) as [Value2] from History WHERE Datetime ='2010-1-1 10:12'      and Tagname ='tag2')  as v2

否则你必须将它转换为整数或任何你想要的数字类型

Answer 4

select h1.value - h2.value
from History h1
inner join History h2 on h1.Datetime = '2010-1-1 10:10' and Datetime ='2010-1-1 10:12'

如何从两个select语句中减去值

4 个答案: