### About the Series ...

This is the twenty-first 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

**and**

*Books Online***.**

*Samples*### What We Accomplished in our Last Article

In the
last article of the series, ** Subset
Functions: The Tail() Function**, we
continued our group of three articles surrounding functions whose primary
purpose is to perform operations on

*subsets*. We introduced the

**Tail()**function, with which we can return a subset from the

*end*of a set. 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, following the approach we have used throughout the series.

In our practice set, we intentionally replicated the
requirements we had simulated in working with the **Head()** function in the
article that preceded it, so as to compare the **Tail()** and **Head()**
functions, and to note their similarities in operation, as well as to contrast
the results datasets they returned. Throughout the practice examples, we
briefly discussed the results datasets we obtained with regard to the **Tail()**
function, together with other surrounding considerations.

### Introduction

In
this lesson, we will conclude our "triptych" of articles exposing set
functions that deal specifically with subsets. As we have noted, each function
returns a subset of a larger set, as part of its operation. We began the
subset functions articles with an examination of the **Head()** function,
then explored **Tail()** in the last. As we mentioned in our last session, these
three functions have much in common in the context of usage and operation; covering
them in close proximity allows us to more finely distinguish among them, as
well as to become aware of their similarities, and to better exploit the attributes
we can leverage to meet specific business needs.

In
this article, we will introduce and overview the **Subset()** function. The
general purpose of the **Subset()** function is to return a subset of tuples
from a specified set. We will first comment upon the operation of **Subset()**,
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.