使用+而不是Aggregate(Union)是否可以获得性能提升 [英] Is there a performance gain using + rather than Aggregate(Union

问题描述

我正在MSDN中查看此帖子: http://msdn.microsoft .com/en-us/library/ms145493.aspx

I was looking at this post in MSDN: http://msdn.microsoft.com/en-us/library/ms145493.aspx

它声明+和Union等同于 ...在下面不完全相同，因为如果我选择使用Union，则需要应用Aggregate.

It states that + and Union are equivalent ... not exactly in the following as Aggregate needs to be applied if I choose to use Union.

它更具可读性，但是在选择+而不是Aggregate(Union时，性能会有所提高吗?

It's more readable but is there any performance gain in choosing + over Aggregate(Union ?

WITH 
  MEMBER [Employee].[Employee].[blah] AS 
      [Employee].[Employee].[Amy E. Alberts]
    + 
      [Employee].[Employee].[Garrett R. Vargas] 
  MEMBER [Employee].[Employee].[blahblah] AS 
    Aggregate
    (
      Union
      (
        {[Employee].[Employee].[Amy E. Alberts]}
       ,{[Employee].[Employee].[Garrett R. Vargas]}
      )
    ) 
SELECT 
  [Measures].[Reseller Sales Amount] ON 0
 ,{
    [Employee].[Employee].[Amy E. Alberts]
   ,[Employee].[Employee].[Garrett R. Vargas]
   ,[Employee].[Employee].[blah]
   ,[Employee].[Employee].[blahblah]
  } ON 1
FROM [Adventure Works]
WHERE 
  [Date].[Calendar].[Month].&[2006]&[8];

推荐答案

问题在于+在MDX中用于多种用途:作为数字加法，用于字符串连接以及用作联合运算符.并且，由于成员定义期望一个传递值的表达式，并且您在两个成员之间使用运算符，并且当前度量的值为数字，因此AS使用数字加法.

The issue is that + is used for several purposes in MDX: as numerical addition, for string concatenation, and as union operator. And as the a member definition expects an expression that delivers a value and you use the operator between two members, and the value of the current measure is numerical, AS uses numerical addition.

如果将成员括在大括号中:

If you enclose the members in braces:

  MEMBER [Employee].[Employee].[blah] AS 
      {[Employee].[Employee].[Amy E. Alberts]}
    + 
      {[Employee].[Employee].[Garrett R. Vargas] }

您收到一个错误，提示AS希望+运算符使用字符串或数字表达式.

you get an error that AS expects string or numeric expressions for the + operator.

可能会有很小的性能提升，但是如果当前度量不由sum聚合，结果可能会有所不同，在这种情况下，这等同于将两个成员值相加.

And there is probably a small performance gain, but the result may be different if the current measure is not aggregated by sum, which would be equivalent to adding both member values in this case.

我个人不喜欢出于不同目的使用此运算符重载+，*等. +和*应该限制为数字，可以是整数，浮点数或小数.与Java，JavaScript和.net中的+以及Microsoft SQL和MDX相比，我还希望使用其他字符串连接运算符.标准SQL使用||，Perl使用.，因此有些替代方法可以避免歧义，并且清楚地知道在编写'2' || 1 vs. '2' + 1 vs. 2 + '1' vs. .

I personally do not like this operator overloading of +, * etc. for different purposes. + and * should be restricted to numbers, be it integers, floats, or decimals. I also would also prefer another operator for string concatenation than + in Java, JavaScript, and .net, as well as Microsoft SQL and MDX. Standard SQL uses ||, Perl uses ., so there are alternatives that clearly avoid ambiguities and you clearly know what to expect when you write '2' || 1 vs. '2' + 1 vs. vs. 2 + '1' vs. 2 + 1.

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