SSAS MDX Overview

Last Updated: October 26, 2023

Multidimensional Expressions (MDX) is a query language for OLAP (Online Analytical Processing) databases. It's a powerful tool for retrieving data from and manipulating data in cubes. This article provides a foundational overview of MDX, its core concepts, and its relevance within SQL Server Analysis Services (SSAS).

What is MDX?

MDX is designed to work with multidimensional data structures, often referred to as cubes. Unlike SQL, which operates on tables and rows, MDX navigates hierarchical structures and can perform complex aggregations and calculations across multiple dimensions.

Key Concepts in MDX

Dimensions: These represent categories of data, such as Time, Geography, or Products.
Hierarchies: Within a dimension, data is often organized into hierarchies (e.g., Year -> Quarter -> Month in the Time dimension).
Members: These are individual items within a hierarchy (e.g., "2023" for Year, "North America" for Geography).
Tuples: A tuple is a set of members, one from each of a specified set of dimensions. It represents a single point in the multidimensional space of the cube.
Sets: A set is an ordered collection of tuples. Sets are fundamental to MDX queries, defining the axes of a result set.
Measures: These are the numerical values you want to analyze, such as Sales Amount, Quantity, or Profit.

Basic MDX Query Structure

An MDX query typically consists of two main parts: the SELECT statement and the FROM clause. The SELECT statement defines the data to be returned, usually specifying measures and members for the columns and rows (axes). The FROM clause specifies the cube to query.

Example: Simple MDX Query


SELECT
    { [Measures].[Sales Amount] } ON COLUMNS,
    { [Geography].[Country].Members } ON ROWS
FROM
    [Adventure Works DW]

This query retrieves the "Sales Amount" measure for each country in the "Geography" dimension from the "Adventure Works DW" cube. The `ON COLUMNS` and `ON ROWS` clauses define the axes of the resulting dataset.

Common MDX Functions

MDX offers a rich set of functions for data manipulation, calculation, and navigation. Some common categories include:

Set Functions: Manipulate sets of members or tuples (e.g., Members, Children, NonEmpty).
Numeric Functions: Perform calculations and aggregations (e.g., Sum, Avg, Count).
String Functions: Manipulate string data.
Navigation Functions: Traverse hierarchies (e.g., Parent, Ancestor, Descendants).

Example: Using a Numeric Function


SELECT
    { [Measures].[Sales Amount].CurrentMember.Parent.Name } ON COLUMNS,
    { [Measures].[Sales Amount] * 1.1 } ON ROWS
FROM
    [Adventure Works DW]

This example demonstrates accessing the parent member's name and performing a calculation (increasing Sales Amount by 10%).

MDX in SSAS

In SQL Server Analysis Services, MDX is the primary language for querying data from multidimensional models. SSAS provides a robust environment for designing cubes and deploying them, making MDX essential for business intelligence professionals working with these solutions. Tools like SQL Server Management Studio (SSMS) and Visual Studio allow you to write and execute MDX queries against SSAS cubes.

Conclusion

Understanding MDX is crucial for effectively querying and analyzing data within SSAS multidimensional models. Its ability to handle complex, multidimensional data makes it a powerful language for business intelligence and reporting. While it has a steeper learning curve than SQL, mastering MDX unlocks significant analytical capabilities.