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MS SQL

Posted Jun 14, 2004

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

By William Pearson

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.


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