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 lessons
included, please see my first article, MDX at First Glance: Introduction to MDX Essentials.
Note: Current updates are assumed for MSSQL
Server, MSSQL Server Analysis Services, and the related Books
Online and Samples.
Overview
We
have noted in several articles that, while MDX functions comprise the lion’s
share of the MDX Essential series, numerous operators are
provided within the language. Of the logical, comparison, set, string, and
unary operators provided by MDX, we will examine another logical operator
in this article. The IsLeaf() operator, like other logical operators,
evaluates values and returns a Boolean value. The utility of IsLeaf() becomes
clear when we realize its value in helping us to determine the position of a
member within a dimensional hierarchy. IsLeaf() more specifically
allows us to test if a member is at leaf level, or at the “bottom” level
of the dimension to which it belongs.
In this article, we will concentrate upon the useful IsLeaf()
operator, from the perspective of its use within a calculation. We will
discuss the straightforward purpose of the operator, to ascertain whether
a member is a leaf-level member of a dimension; the manner in which IsLeaf()
manages to do this; and ways we can leverage the operator to support effective
conditional logic to meet various business needs within our own environments.
Along
with an introduction to the IsLeaf() operator, this lesson will include:
-
an examination of the syntax surrounding the operator;
-
illustrative examples of uses of the operator in practice
exercises;
-
a brief discussion of the MDX results obtained within each of the
practice examples.
The IsLeaf() Operator
Introduction
According to the Books
Online, the IsLeaf() operator “returns a value whether or not a
specified member is a leaf member.” A Boolean value of “True” is returned
if the member expression to which it is applied is a leaf member;
otherwise IsLeaf() returns “False.” IsLeaf() is often
employed in conjunction with the IIF function to conditionally return
data, such as a member or members (for example, children of a selected member,
if they exist, or the selected member if it has no children), or values.
We will examine in detail the
syntax for the IsLeaf() operator after our customary overview in
the Discussion section that follows. Following that, we will conduct
practice examples within a couple of scenarios, constructed to support a
hypothetical business need that illustrates a use for the operator. This will
afford us an opportunity to explore some of the basic options that IsLeaf() can
offer the knowledgeable user. Hands-on practice with IsLeaf(), where we
will create queries that employ the function, will help us to activate what we have
learned in the Discussion and Syntax sections.
Discussion
To restate our initial description
of its operation, IsLeaf() returns “True” if a specified member expression
represents a leaf (or “level 0”) member; otherwise, the operator
returns “False.” We can use IsLeaf() to apply conditional
logic based upon the location or existence of members. As we have noted to
be the case with most MDX functions and operators, pairing the IsLeaf()
operator with other MDX operators and functions can help us to leverage its
power even further.
Let’s look at syntax specifics to further clarify the
operation of IsLeaf().
Syntax
Syntactically, we employ the IsLeaf()
operator by specifying the member expression in parentheses to the
immediate right of the operator. The operator takes the member expression
which is appended to it as its argument, and returns True if the member
denoted by the member expression is a leaf member (or, in other
words, the member resides at the lowest (0) level of the dimension). If the
member specified by the member expression is not a leaf
member (or if the member resides at a dimensional level higher than the zero,
or “bottom,” level), a False is returned.
The general syntax is shown in
the following string:
IsLeaf(Member Expression)
Employing IsLeaf() is, in itself, straightforward.
As we have noted, we simply place the member expression under
consideration in the parentheses to the right of the operator. As an example,
within a query executed against the sample Adventure Works cube, for a
dimension named Sales Territory (with a hierarchy of the same name), the
following pseudo-expression:
IsLeaf([Sales Territory].[Sales Territory].CURRENTMEMBER)
Returns True if the current member of the Sales
Territory dimension / Sales Territory hierarchy
is at level 0.
We will practice some uses of the IsLeaf() operator
in the section that follows.
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