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Posted Dec 31, 2007

MDX Numeric Functions: The Max() Function - Page 3

By William Pearson

Procedure: Use the Max() Function to Select Peak Sales and the Month in Which They Occur

Having demonstrated the basic operation of Max(), we are ready to address another requirement that the client representatives describe. To detail the requirement, our colleagues have asked us to address a specific, immediate need, although they hope to be able to extrapolate the concepts we introduce to other, similar needs that commonly arise within the organization. Our colleagues have asked that we construct a query that presents a slightly more sophisticated dataset, and uses the Max() function in a way that differs from our previous example, where we simply retrieved a maximum measure value for a specified set.

Max(), of course, can be used in numerous ways that lie beyond the obvious selection of the”largest number” or “biggest amount” for a set we use as a basis in the function. We often, for instance, use the function to select the “last” (or “greatest”) month (or other Date period), as an example where we have conducted activity or maintain a balance. The business requirement that the client representatives communicate next contains an element of such a need, as we shall see.

Our colleagues tell us that they wish to support the capability of Logistics users to report upon and analyze peak sales of the Resellers, with which Adventure Works maintains relationships, to market and distribute its products. To begin, they wish to be able to generate a dataset that presents the highest monthly sales values for Resellers who have completed sales within the last Calendar Year, 2003. Moreover, they wish to present, alongside this “peak sales” value, the period within which the sales were achieved (which they wish to label “Peak Period” within the returned dataset), for ease of use for immediate needs, as well as to support some charts they wish to create in Reporting Services at a later time. The client representatives make us aware that they wish to screen out Resellers who have no activity at all over the given Calendar Year, simply to streamline reports and make them more compact.

We explain that the Max() function promises to be useful in generating the desired presentation. We confirm our understanding of the foregoing needs, as well as our conclusion that we have happened upon a great opportunity to both assist the client in meeting its immediate needs as well as to provide examples that leverage the MDX Max() function. We set out to craft a query that relies upon Max(), in conjunction with other the MDX functions, to meet the business need.

The basic Max() function involved will be housed within a couple of calculated members, which we will call Peak Sales and Peak Period, respectively. We will then employ the calculated members within a core query that arranges the information it retrieves in the manner requested. Our query will be constructed as described in the following procedure.

1.  Select File --> New from the main menu.

2.  Select Query with Current Connection from the cascading menu that appears next, as depicted in Illustration 5.

Illustration 5: Create a New Query with the Current Connection ...

A new tab, with a connection to the Adventure Works cube (we can see it listed in the selector of the Metadata pane, once again) appears in the Query pane.

3.  Type (or cut and paste) the following query into the Query pane:

-- MDX062-2 More Sophisticated Example of MAX() Function in Use



   [Measures].[Peak Sales]


   'MAX(DESCENDANTS( [Date].[Calendar].[Calendar Year].[CY 2003],


          [Measures].[Reseller Sales Amount]


   [Measures].[Peak Period]



    MAX([Date].[Calendar].[Month].MEMBERS, [Measures].[Reseller Sales Amount]) > 0, 


             DESCENDANTS( [Date].[Calendar].[Calendar Year].[CY 2003],



         [Measures].[Reseller Sales Amount]).ITEM(0).NAME, null



    {[Measures].[Peak Sales], [Measures].[Peak Period]} ON AXIS(0),


   {[Reseller].[Reseller Type].[Reseller].MEMBERS}

    ON AXIS(1)


   [Adventure Works]

The Query pane appears, with our input, as shown in Illustration 6.

Illustration 6: Our Second Query in the Query Pane ...

We note that we have taken steps, within the conditional element of the Peak Period calculated measure, to present a null in place of the default that would display (the first period, January, of 2003) were we to simply to allow default behavior. This allows us to screen null rows out via Non Empty. For those Resellers experiencing at least one sale within Calendar Year 2003, we derive a Peak Sales value using the Max() function, specifying the members of the Month level of the Date dimension (Calendar hierarchy) as the Set Expression across which the Numeric Expression representing the Reseller Sales Amount measure is evaluated.

We use the TopCount() function within the creation of the Peak Period calculated measure, effectively stating that we wish to retrieve the first, or “topmost” values that occur within the Months (we use the Descendants() function to specify that the query focus upon the relevant Month level members of Calendar Year 2003)

4.  Execute the query by clicking the Execute button in the toolbar.

The Results pane is, once again, populated by Analysis Services. This time, the dataset partially depicted in Illustration 7 appears.

Illustration 7: Results Dataset – Max() Leveraged to Deliver More Sophistication (Partial View)

In the returned dataset, we see the list of Resellers who have been evaluated as having sales activity in at least one period of Calendar Year 2003. Juxtaposed with these names, we observe the two calculated members we have constructed, Peak Sales (containing the primary use of the Max() function) and Peak Period (within which we make referential use to the Max() function as it exists in the first calculated member – primarily to support conditional logic that nulls the derived Peak Period date, and which allows it to be filtered out via Non Empty). The second calculated member also leverages the combination of the .Item() and .Name functions to generate the month and year format that represents the Peak Period output in the dataset.

NOTE: For more detail surrounding the TopCount() function, see Basic Set Functions: The TopCount() Function, Part I and Basic Set Functions: The TopCount() Function, Part II . For information on IIF(), see String / Numeric Functions: Introducing the IIF() Function and String / Numeric Functions: More on the IIF() Function. For exposure to the Descendants() function, see various articles throughout the MDX Essentials series.

For information on the .Item() function, see Basic Member Functions: The .Item() Function. For an introduction to the .Name function, see String Functions: The .Name Function. For examples of the use of Non Empty, see various articles throughout this series. Finally, for an introduction to the .Members function, see my article MDX Members: Introducing Members and Member.

5.  Select File -> Save MDXQuery2.mdx As ..., name the file MDX062-002.mdx, and place it in the same location used to store the earlier query.

To corroborate the operation of the solution we have proposed above, let’s examine the sales figures concerned for a given reseller over all periods in the year under examination. From this quick test dataset, we can see that our calculated members (each leveraging the Max() function) have served us as expected, both in selection of the appropriate value for Peak Sales and the appropriate month for Peak Period.

6.  Select File --> New from the main menu, as we did earlier.

7.  Select Query with Current Connection from the cascading menu that appears next, once again.

A new tab, with a connection to the Adventure Works cube appears in the Query pane, as before.

8.  Type (or cut and paste) the following query into the Query pane:

-- MDX062-3 "Check Query" to Ascertain Solution Effectiveness



     {DESCENDANTS( [Date].[Calendar].[Calendar Year].[CY 2003],


            {[Measures].[Reseller Sales Amount]} 


     ON AXIS(0),

{[Reseller].[Reseller Type].[Reseller].[Best o' Bikes]: 

   [Reseller].[Reseller Type].[Reseller].[Bicycle Exporters]}

    ON AXIS(1)


  [Adventure Works]

The Query pane appears, with our input, as shown in Illustration 8.

Illustration 8: Verifying Our Results with a “Test Data” Query

We have simply constructed a query to generate the Calendar Year 2003 monthly values for Reseller Sales Amount for a couple of the organization’s resellers, Best o’ Bikes and Bicycle Exporters. We will be able, thereby, to easily identify the “highest value” of each that represents Peak Sales value among the months. We can then also see, at a moment’s glance, the month in which these sales took place (and thus confirm the Peak Period involved). We can then compare the results of our sample to the values delivered by our two calculated members, Peak Sales and Peak Period, from the last dataset retrieved by the last query, to determine accuracy – and thereby verify the effectiveness of our approach.

NOTE: For more detail surrounding the CrossJoin() function, see Basic Set Functions: The CrossJoin() Function. For a discussion of the Range (“:”) operator, see my article MDX Operators: The Basics. Both articles are members of my MDX Essentials series at Database Journal.

9.  Execute the query by clicking the Execute button in the toolbar.

The Results pane is, as before, populated by Analysis Services. The dataset depicted in Illustration 9 appears.

Illustration 9: Results Dataset – Confirmation Query

In the returned dataset, we see the values we have discussed appearing for each month in Calendar Year 2003 for each sample Reseller. We also note that the values presented by the Peak Sales calculated member in our solution for each of the two Resellers agrees to what we can easily see is the largest value within the confirmation dataset, and that the month within which the “highest month’s sales” took place in the confirmation dataset agrees to the Peak Period month returned in our solution. The comparisons appear as shown in composite Illustration 10.

Illustration 10: Results Datasets Composite – Indicating That Our Solution is Effective

The Logistics department representatives express satisfaction with the results, and confirm their understanding of the operation of the Max() function within the context we have presented, among other uses we have discussed in earlier sections. We suggest to our client colleagues that, among numerous possibilities, the Resellers (single, multiple, or ranged, etc.), as well as various components of the Date dimension (Calendar or Fiscal Hierarchy, Year, Semesters, Quarters, and so forth), and even the “number of highest values” (say, for example, “top two” or “top five”, etc.), and other components of our query might be parameterized, within their Reporting Services environment. Moreover, we emphasize, we might add other capabilities within the ultimate reporting dataset query.

Suffice it to say that, assuming an “above ordinary” knowledge of the various layers of the Microsoft integrated BI solution, one can obtain many powerful capabilities and features, and knowing “where to put the intelligence” within the sometimes multiple choices can mean highly tuned performance and effective solutions for consumers throughout our organizations. For more of my observations on this subject see Multi-Layered Business Solutions ... Require Multi-Layered Architects.

10.  Experiment with the “test query,” as desired, to examine and compare the values for other Resellers to those delivered by the previous query via the Max() function.

11.  Select File -> Save MDXQuery3.mdx As ..., name the file MDX062-003.mdx, and place it in the same location used to store the earlier query, if and when desired.

12.  Select File -> Exit to leave the SQL Server Management Studio, when ready.

Summary ...

In this article, we introduced and explored the MDX Max() function, one of several aggregate functions available within the MDX toolset, whose general purpose is to deliver a maximum value of a numeric expression that is evaluated over a set. We emphasized that Max() can be leveraged in a wide range of activities, from the “generation of maximums” from simple sets of dimensional members to multidimensional juxtapositions we can compose to deliver even more sophisticated results. Moreover, we learned that Max() can serve as an excellent tool to support sophisticated conditional logic, as well as other calculations, to deliver exactly the analysis and reporting presentations required by our clients and employers.

We examined the syntax involved with Max(), and then undertook a couple of illustrative practice examples of uses for the function, generating queries that capitalized upon its capabilities. Throughout our practice session, we briefly discussed the results datasets we obtained from each of the queries we constructed, as well as extending our discussion to other possible options and uses for the concepts we exposed.

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

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