Set Functions: The DrillDownLevelTop() and DrillDownLevelBottom() Functions
March 6, 2006
About the Series ...
This article is a member of the series, MDX Essentials. The series is designed to provide hands-on application of the fundamentals of the Multidimensional Expressions (MDX) language, with each tutorial progressively adding features designed to meet specific real-world needs.
For more information about the series in general, as well as the software and systems requirements for getting the most out of the member lessons, please see Set Functions: The DRILLDOWNMEMBER() Function, where important information is detailed regarding the applications, samples and other components required to complete our practice exercises.
In this article, we will continue the examination of "MDX for drilling up and down" that we began in Set Functions: The DrillDownMember() Function. We have discussed the nature of drilling, in general, in previous articles of our sub-series, stating that it comprises an analytical technique through which means an information consumer can maneuver between summarized ("drilling up") and detailed ("drilling down") levels of data. We noted that drilling up or down occurs along the lines of drilling paths that are defined within the structure of our cubes, and which are often specified by the cube's dimensional hierarchies. We mentioned, too, that these paths can be based upon alternative relationships that exist within or between dimensions.
In our last article, Set Functions: The DrillDownLevel() Function, we introduced the "primary," level-directed MDX drilldown function, DrillDownLevel(). We stated that it supports the capability of Analysis Services to meet the common need for drilldown from a given Set to members within the next lower level, or to a level which we can specify using an optional Level Expression or, alternatively, an optional Index. Through our overview, discussion, examination of the syntax, and hands-on practice session with the function, we discovered how DrillDownLevel() drills down the members of a set to a lower level, and additionally offers us the flexibility to specify which level below a given member in the set, as well as providing a means whereby we can specify an index to further control the behavior of the DrillDownLevel() function in targeting a specific level. We focused on several ways to leverage the function in our queries and, ultimately, in reporting and other end applications, to meet the business needs of organizational information consumers.
In this article we will examine two specialized set functions that are based upon the principles underlying DrillDownLevel(). DrillDownLevelTop() and DrillDownLevelBottom() are both similar to the DrillDownLevel() function. However, instead of behaving like DrillDownLevel(), in its inclusion of all children for each member within the specified Level Expression, DrillDownLevelTop() returns the topmost (specified) number of child members for each member, while the DrillDownLevelBottom() function returns the bottommost (specified) number of child members for each member.
Like the DrillDownLevel() function, both DrillDownLevelTop() and DrillDownLevelBottom() can be used in conjunction with tuples within the sets, as well as members. In a manner similar to DrillDownMember(), among numerous other functions that we have examined in the MDX Essentials series, DrillDownLevelTop() and DrillDownLevelBottom() can each be useful in a host of different reporting and analysis applications. Like other "navigational" functions of their feather (virtually all of which we examine in other articles of this and other series') each of these two drilldown functions allows us to exercise a great deal of presentation sleight of hand, in working with MDX in Analysis Services, as well as within Reporting Services and various other reporting applications that can access an Analysis Services cube.
The DrillDownLevelTop() and DrillDownLevelBottom() functions can be leveraged, within and among the various "layers" of the Microsoft integrated Business Intelligence solution, to support sophisticated presentations and features. We will introduce the functions, commenting upon the operation of each and touching upon examples of effects that we can employ each to deliver. As a part of our discussion, we will: