MDX Essentials: The CROSSJOIN() Function: Breaking Bottlenecks

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

Overview

In this article, we will return to a function we introduced
in an earlier article, CROSSJOIN(), whose mission it is to combine two
sets of dimension members into one. We will discuss how CROSSJOIN()
works in general, and then discuss how its performance can become an issue in
medium to large-sized data sets. We will then undertake a multiple-step
practice example intended to assist us in gaining an understanding of the
issues, before exposing approaches to minimizing the performance overhead that
we can encounter in using CROSSJOIN() to reach our reporting and
analysis needs.

To accomplish this objective, we will undertake the following
steps in this article:

  • Create a copy of the Warehouse
    sample cube for use in our practice exercise;

  • Prepare the cube further by
    processing;

  • Discuss the
    operation of the CROSSJOIN() function, and factors that may make its use
    suboptimal in our queries;

  • Enhance a
    suboptimal query employing a CROSSJOIN() function by substituting NONEMPTYCROSSJOIN();

  • Provide
    further enhancement by leveraging the set count parameter
    in the NONEMPTYCROSSJOIN()
    function;

  • Explain the results we obtain from the steps we take to
    accomplish the solution.
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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