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.
Overview
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:
- Examine the syntax surrounding the functions;
-
Undertake illustrative examples of the uses of the functions in
practice exercises; -
Briefly discuss the results datasets we obtain in the practice
examples.
