MDX Essentials: MDX Member Functions: "Relative" Member Functions - Page 5

June 2, 2003

The .NextMember Function

The .NextMember function, according to the Analysis Services Books Online, "returns the next member in the level that contains a specified member." In other words, the function returns the member in the dimensional hierarchy occurring later at the same level as the specified member. The .NextMember function works in a manner similar to the .PrevMember function, except that, instead of returning the member that occurs at the same level as the specified member, earlier in the hierarchy, it returns the same-level member that follows the specified member within the hierarchy.

Discussion:

The utility of the .NextMember function is intuitive for purposes of meeting business needs that include the example we have discussed earlier, the determination of change over a given pair of periods (next year over the current year, and so forth).

Syntax

Let's look at an example to familiarize ourselves with the syntax.

 WITH 
 MEMBER [Measures].[Warehouse Margin] AS
 '[Measures].[Warehouse Sales] - [Measures].[Warehouse Cost]'
 
 
 SELECT
     
    {([Time].CurrentMember),([Time].NextMember)} ON COLUMNS,
              {([Warehouse].[Country].USA)} ON ROWS
 
 FROM Warehouse
 
 WHERE ([Measures].[Warehouse Margin])

The result dataset returned would appear as shown in Illustration 6 below:

The .NextMember function is used within the definition of the calculated member, inside the WITH clause. In this case, we are specifying the next member of the Time dimension at the year level, which turns out to be 1998, because, unlike in previous examples, we have specified no slicer in the WHERE clause. The result is that the current member for the year is the default, 1997. Therefore, the "next" member of the time dimension at the same hierarchical level is 1998. We note that the results we obtain appear consistent with those obtained in previous queries, from slightly different approaches.

Practice

Let's practice with the .NextMember function, combining its use with that of the .CurrentMember function, in a manner that assists us in performing analysis of performance from one year to the next, just as we have done before. We return to the MDX Sample Application, creating a new query for the purposes of this exercise.

-- MDX08-3:  Tutorial Query No. 3
WITH 
   MEMBER [Measures].[Margin Base Year] AS
   '([Time].CurrentMember , [Measures].[Warehouse Sales])-([Time].CurrentMember, 
       [Measures].[Warehouse Cost])'
   MEMBER [Measures].[Margin Base + 1] AS
   '([Time].NextMember , [Measures].[Warehouse Sales])-([Time].NextMember, 
    [Measures].[Warehouse Cost])'
   MEMBER [Measures].[$ Change] AS
   '([Time].CurrentMember , [Measures].[Margin Base + 1]) - ([Time].CurrentMember, 
     [Measures].[Margin Base Year])'

SELECT

   { [Measures].[Margin Base Year],  [Measures].[Margin Base + 1], [Measures].[$ Change]} ON 
       COLUMNS,
   {([Warehouse].[Country].[USA])} ON ROWS

FROM Warehouse

The query runs and the result dataset appears, as shown in Illustration 7.

The query delivers the results as requested; we see the three related calculated measures, Margin Base Year, Margin Base + 1, and $ Change; the latter, $ Change, is again a calculated measure that is made up of the subtraction of one of the first two calculated measures from the other.

We see that the behavior of the .NextMember function is, therefore, very similar to that of the .PrevMember function, only it acts, conceptually, "in the opposite direction." We can also readily see the potential usefulness of the function with regard to its capability to support the analysis of measures that change over time, among other uses within our data sources.

Next in Our Series ...

In this lesson, we began an overview of additional "relative" member functions, expanding upon our earlier exposure to the powerful .Members function, and extending our exploration to the .CurrentMember, .PrevMember and .NextMember functions. We introduced calculated members briefly, as an avenue to demonstrating the use of the "relative" member functions. As we noted in the Calculated Members section above, we will take up calculated members in far more detail as the series progresses; I hope that our initial exposure to them in this article, and our recurring use of them going forward to achieve various objectives, will make their characteristics and uses familiar as we progress in the series.

In our next lessons, we will introduce the time series functions group. As we discussed in this lesson, many business requirements revolve around the performance of analysis within the context of time. We saw simple approaches to meeting examples of these requirements by using the CurrentMember, .PrevMember and .NextMember functions in this lesson, mainly because the time dimension provides an intuitive way to demonstrate many functions such as these.

Because of pervasive business needs to analyze data within the context of time, MDX provides a specialized group of time series functions to meet these needs. In the next lesson, we will overview the PeriodsToDate() function, then we will discuss the specialized "shortcut" functions that are based upon it, including the YTD(), QTD(), MTD(), and WTD(). In subsequent lessons, we will explore other time series functions and expressions, together with other capabilities of MDX to help us to meet typical business needs.

» See All Articles by Columnist William E. Pearson, III

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