Question

我想在sql中获得数字x的正面部分。这意味着如果x> 0则结果为x，否则为零。我的意思是在聚合函数之后使用它。

select 1 as num, 200 as weight into #table
insert into #table values
(8, 100),
(10, 200),
(11, -300),
(20, -100);

直到现在我一直在使用以下内容：

select sum(num * weight)/sum(weight) as Result, 
       IIf(sum(num * weight)/sum(weight)>0, sum(num * weight)/sum(weight), 0) as PositivePartResult    
from #table

但是，功能变得越来越不明确。是否有内置函数可以在不重复公式的情况下获得相同的结果？

Answer 1

编写相同查询的另一种方法是：

select Result,
       case when Result > 0 Then Result else 0 end as  PositivePartResult 
       from 
       (
          select sum(num * weight)/sum(weight) as Result       
          from #table
       )T

Answer 2

您可以计算内联值，或者，如果您经常这样做，请创建用户定义的函数：

create function PositiveValue( @N as Int )
  returns Int as
  begin
    return ( Sign( @N ) + 1 ) / 2 * @N;
  end;
go

declare @Samples as Table ( N Int );
insert into @Samples ( N ) values ( -42 ), ( -1 ), ( 0 ), ( 1 ), ( 42 );

select N, ( Sign( N ) + 1 ) / 2 * N as PositiveValue1, dbo.PositiveValue( N ) as PositiveValue2
  from @Samples;

-- drop function dbo.PositiveValue;

SQL - 正部分函数（x）^ +

2 个答案: