This section provides comprehensive documentation on Multidimensional Expressions (MDX) queries for Microsoft SQL Server Analysis Services. MDX is a powerful query language used to retrieve data from multidimensional data sources, such as OLAP cubes.

Introduction to MDX

MDX is designed for querying data within a multidimensional database structure. It allows you to navigate through hierarchies, slice and dice data, perform complex calculations, and return results in a tabular format suitable for reporting and analysis.

Key Concepts

  • Cubes: The fundamental data structure in Analysis Services, containing measures and dimensions.
  • Dimensions: Hierarchical structures representing business entities like Time, Geography, or Products.
  • Hierarchies: Levels within a dimension, allowing drill-down and roll-up operations.
  • Measures: Numeric values that are aggregated, such as Sales Amount or Quantity.
  • Members: Specific elements within a dimension or hierarchy (e.g., '2023' in the Time dimension, 'North America' in the Geography dimension).
  • Tuples: A set of members, one from each of one or more dimensions, defining a specific point in the cube.
  • Sets: An ordered collection of tuples.

Basic MDX Query Structure

An MDX query typically consists of the following clauses:

  • SELECT: Specifies the axes (rows and columns) for the query result.
  • FROM: Identifies the cube or virtual cube to query.
  • WHERE: Filters the data by defining a context (slicer).

Example: Simple Sales Query

This query retrieves the total sales amount for each product category on the rows and for the year 2023 on the columns.

SELECT
    {[Measures].[Sales Amount]} ON COLUMNS,
    [Product].[Category].Members ON ROWS
FROM
    [Adventure Works]
WHERE
    ([Date].[Calendar Year].&[2023])

MDX Functions and Statements

MDX offers a rich set of functions for data manipulation, calculation, and navigation.

Common Functions

  • Aggregate functions: SUM, AVG, COUNT, MAX, MIN.
  • Set functions: { } (set constructor), UNION, INTERSECT, EXCEPT.
  • Member functions: Member(), Parent(), Children(), Level().
  • Navigation functions: NextMember(), PrevMember(), Ancestor().

Calculated Members

You can define calculated members to perform custom calculations directly within your MDX query. These are typically defined in the WITH clause.

WITH MEMBER [Measures].[Profit Margin] AS
    ([Measures].[Sales Amount] - [Measures].[Cost Amount]) / [Measures].[Sales Amount]
SELECT
    {[Measures].[Sales Amount], [Measures].[Profit Margin]} ON COLUMNS,
    [Product].[Category].Members ON ROWS
FROM
    [Adventure Works]
Note: Understanding the structure of your cube, including dimensions, hierarchies, and their relationships, is crucial for writing effective MDX queries.

Advanced MDX Topics

  • Sub-cubes and Slicers
  • Recursive Hierarchies
  • User-Defined Functions (UDFs)
  • MDX Scripting (within cube definition)
  • Performance Tuning for MDX Queries

Explore the links below for detailed syntax, function references, and practical examples.