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

About the Series …

This is the twentieth 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 systems 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, Subset
Functions: The Head() Function
, we
introduced the Head() function, whose general purpose is to return a
specified number of elements from the beginning of a set, preserving natural
order. We commented upon the operation of the function, and then examined its
syntax. Next, we undertook practice examples with the function, based upon
hypothetical business requirements. Our practice included the creation of
queries to meet illustrative business needs, as well as demonstrations of the
manner in which the Head() function handles various numeric expression
input scenarios. Throughout the practice examples, we briefly discussed the
results datasets we obtained with regard to the Head() function,
together with other surrounding considerations.

Introduction

In
this lesson, we continue 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. Having covered the Head()
function in the previous article, we will introduce the Tail() function
in this article, then follow it with the Subset() function in the next
article. As we mentioned in our last session, these three functions have much
in common with regard to usage and operation; covering them in close proximity
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 Tail() function is to return the last specified
number
of elements in a set. We will introduce the Tail()
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 of 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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