MDX Essentials: Basic Set Functions: Subset Functions: The Head() Function

About the Series …

This is the nineteenth article 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 system requirements needed for getting the most out of the
lessons included, please see the first article, MDX at
First Glance: Introduction to MDX Essentials
.

Note: Service Pack 3 updates are assumed for MSSQL
Server 2000
, MSSQL Server 2000 Analysis Services, and the related Books
Online
and Samples.

What We Accomplished in our Last Article

In the
last article of the series,
Basic
Set Functions: The CrossJoin() Function
, we explored the highly popular CrossJoin() function.
We discussed the general purpose of the function, to allow us to produce all
possible combinations of two sets, and cited its common use to "collapse"
two or more dimensions onto a single axis for purposes of presenting
multidimensional data in a two-dimensional matrix.

We began by introducing
CrossJoin(), commenting upon its operation and touching upon performance
considerations at a general level. We examined the syntax surrounding the
function, and then began practice exercises to illustrate the operation of the
function, within hypothetical scenarios where we described a business need. We
then set about solving the need with a straightforward MDX query that exploited
the CrossJoin() function. Finally, we briefly discussed the results
datasets we obtained in the practice examples.

Introduction

In
this lesson, we will begin a "triptych" of articles that expose set
functions that deal specifically with subsets – that is, each function returns
a subset of a larger set as part of its operation. We will introduce the Head()
function in this article, then follow it with the Tail() function in the
subsequent article. The last of the three subset functions that we will
investigate will be, unsurprisingly, the Subset() function. These three
functions have much in common with regard to usage and operation, and covering
them in this fashion will allow us to more finely distinguish among them, to
exploit the attributes we can leverage to meet specific business needs.

The
general purpose of the Head() function is to return the first specified
number
of elements in a set. We will introduce the Head()
function, commenting upon its operation, and then we will:

  • Examine the syntax surrounding the function;

  • Undertake illustrative examples of the uses of the function in
    practice exercises;

  • Briefly discuss the results datasets we obtain in the practice
    examples.
William Pearson
William Pearson
Bill has been working with computers since before becoming a "big eight" CPA, after which he carried his growing information systems knowledge into management accounting, internal auditing, and various capacities of controllership. Bill entered the world of databases and financial systems when he became a consultant for CODA-Financials, a U.K. - based software company that hired only CPA's as application consultants to implement and maintain its integrated financial database - one of the most conceptually powerful, even in his current assessment, to have emerged. At CODA Bill deployed financial databases and business intelligence systems for many global clients. Working with SQL Server, Oracle, Sybase and Informix, and focusing on MSSQL Server, Bill created Island Technologies Inc. in 1997, and has developed a large and diverse customer base over the years since. Bill's background as a CPA, Internal Auditor and Management Accountant enable him to provide value to clients as a liaison between Accounting / Finance and Information Services. Moreover, as a Certified Information Technology Professional (CITP) - a Certified Public Accountant recognized for his or her unique ability to provide business insight by leveraging knowledge of information relationships and supporting technologies - Bill offers his clients the CPA's perspective and ability to understand the complicated business implications and risks associated with technology. From this perspective, he helps them to effectively manage information while ensuring the data's reliability, security, accessibility and relevance. Bill has implemented enterprise business intelligence systems over the years for many Fortune 500 companies, focusing his practice (since the advent of MSSQL Server 2000) upon the integrated Microsoft business intelligence solution. He leverages his years of experience with other enterprise OLAP and reporting applications (Cognos, Business Objects, Crystal, and others) in regular conversions of these once-dominant applications to the Microsoft BI stack. Bill believes it is easier to teach technical skills to people with non-technical training than vice-versa, and he constantly seeks ways to graft new technology into the Accounting and Finance arenas. Bill was awarded Microsoft SQL Server MVP in 2009. Hobbies include advanced literature studies and occasional lectures, with recent concentration upon the works of William Faulkner, Henry James, Marcel Proust, James Joyce, Honoré de Balzac, and Charles Dickens. Other long-time interests have included the exploration of generative music sourced from database architecture.

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