MDX Basics for Beginners

Welcome to the fundamental concepts of Multidimensional Expressions (MDX), a powerful query language for Microsoft SQL Server Analysis Services. This article is designed for beginners looking to understand the core syntax and logic behind MDX queries.

What is MDX?

MDX is used to retrieve data from multidimensional cubes. Unlike SQL, which is designed for relational databases, MDX is optimized for navigating hierarchical data structures and performing complex analytical operations like slicing, dicing, and aggregation across multiple dimensions.

Key Concepts

Before diving into queries, let's understand some essential MDX terms:

• Cube: A multidimensional data structure that organizes data into measures and dimensions.
• Dimension: Represents a category of data (e.g., Time, Geography, Product).
• Hierarchy: A structure within a dimension that allows for drill-down and roll-up operations (e.g., Year -> Quarter -> Month).
• Level: A specific step in a hierarchy (e.g., Year is a level in the Time hierarchy).
• Member: An individual item within a level (e.g., '2023' is a member of the Year level).
• Measure: A numerical value that can be aggregated (e.g., Sales Amount, Quantity Sold).

Basic MDX Syntax

An MDX query typically consists of the following clauses:

• SELECT: Defines the data to be returned.
• FROM: Specifies the cube to query.
• WHERE: Filters the data based on specific criteria.

The SELECT Clause

The SELECT clause specifies what you want to see. It uses axes (ON COLUMNS, ON ROWS) to define the structure of the result set.

SELECT
    {[Measures].[Internet Sales Amount]} ON COLUMNS,
    {[Date].[Calendar Year].Members} ON ROWS
FROM
    [Adventure Works DW2019]

In this example:

• [Measures].[Internet Sales Amount] is a member of the Measures dimension, placed on the columns axis.
• [Date].[Calendar Year].Members retrieves all members of the Calendar Year level within the Date dimension and places them on the rows axis.
• [Adventure Works DW2019] is the name of the cube being queried.

The WHERE Clause (Slicer)

The WHERE clause acts as a slicer, filtering the entire result set without consuming an axis.

SELECT
    {[Measures].[Internet Sales Amount]} ON COLUMNS,
    {[Date].[Calendar Year].Members} ON ROWS
FROM
    [Adventure Works DW2019]
WHERE
    ([Product].[Category].&[1], [Geography].[Country].&[USA])

Here, the query is filtered to show sales only for Product Category 1 and Country USA. The .&[...] syntax is used to reference specific members by their unique name (often called a Key).

Navigating Hierarchies

MDX excels at navigating hierarchies. You can reference specific members, parent members, child members, and siblings.

Example: Parent and Children

To get the sales for a specific country and its sub-regions:

SELECT
    {[Measures].[Internet Sales Amount]} ON COLUMNS,
    [Geography].[Country].&[USA].Children ON ROWS
FROM
    [Adventure Works DW2019]
WHERE
    ([Date].[Calendar Year].&[2023])

This query retrieves sales for all countries that are children of the 'USA' member (which might be a mistake in common hierarchy design, but illustrates the concept; typically you'd use country as a top level and states/regions as children). A more practical example would be getting sales for all months within a specific year:

SELECT
    {[Measures].[Internet Sales Amount]} ON COLUMNS,
    [Date].[Calendar].&[2023].Children ON ROWS
FROM
    [Adventure Works DW2019]

Conclusion

This introduction covered the basic structure of an MDX query, including SELECT, FROM, and WHERE clauses, along with fundamental concepts like dimensions, hierarchies, and members. Mastering these basics will pave the way for more complex analytical queries.