The Basic MDX Query

A basic Multidimensional Expressions (MDX) query is structured in a fashion similar to the following example:

SELECT [<axis_specification>
       [, <axis_specification>...]]
  FROM [<cube_specification>]
[WHERE [<slicer_specification>]]

Basic MDX Syntax - SELECT Statement

In MDX, the SELECT statement is used to specify a dataset containing a subset of multidimensional data. To discuss the various syntax elements of the MDX SELECT statement, this topic presents a basic MDX query example and breaks it down into its syntax elements, discussing the purpose and structure of each element.

To specify a dataset, an MDX query must contain information about:

• The number of axes. You can specify up to 128 axes in an MDX query.
  
  
• The members from each dimension to include on each axis of the MDX query.
  
  
• The name of the cube that sets the context of the MDX query.
  
  
• The members from a slicer dimension on which data is sliced for members from the axis dimensions.

This information can be complex. As you will see in this topic, MDX syntax can provide such information in a simple and straightforward manner, using the MDX SELECT statement.

Basic MDX Query Example

The following MDX query example is used to discuss the various parts of basic MDX SELECT statement syntax:

SELECT
   { [Measures].[Unit Sales], [Measures].[Store Sales] } ON COLUMNS,
   { [Time].[1997], [Time].[1998] } ON ROWS
FROM Sales
WHERE ( [Store].[USA].[CA] )

The basic MDX SELECT statement contains a SELECT clause and a FROM clause, with an optional WHERE clause.

The SELECT clause determines the axis dimensions of an MDX SELECT statement. Two axis dimensions are defined in the MDX query example. For more information about the construction of axis dimensions in a SELECT clause, see Specifying the Contents of an Axis Dimension.

The FROM clause determines which multidimensional data source is to be used when extracting data to populate the result set of the MDX SELECT statement. For more information about the FROM clause, see SELECT Statement.

The WHERE clause optionally determines which dimension or member to use as a slicer dimension; this restricts the extracting of data to a specific dimension or member. The MDX query example uses a WHERE clause to restrict the data extract for the axis dimensions to a specific member of the Store dimension. For more information about the construction of a slicer dimension in a WHERE clause, see Specifying the Contents of a Slicer Dimension.

The MDX SELECT statement supports other optional syntax, such as the WITH keyword, and the use of MDX functions to construct members by calculation for inclusion in an axis or slicer dimension. For more information about the MDX SELECT statement, see SELECT Statement.

The syntax format of the MDX SELECT statement is similar to that of SQL syntax; however, you will note several obvious differences:

• MDX syntax distinguishes sets by surrounding tuples or members with braces (the { and } characters.) For more information about member, tuple, and set syntax, see Members, Tuples, and Sets.
  
  
• MDX queries can have up to 128 axis dimensions in the SELECT statement, but only the first 5 axes have aliases. An axis can be referred to by its ordinal position within an MDX query or by its alias, if it has an alias assigned to it. In the MDX query example, the COLUMNS and ROWS axis aliases are used. The MDX query could also have been written in the following fashion, using the ordinal position of each axis:

  SELECT
     { [Measures].[Unit Sales], [Measures].[Store Sales] } ON AXIS(0),
     { [Time].[1997], [Time].[1998] } ON AXIS(1)
  FROM Sales
  WHERE ( [Store].[USA].[CA] )
  

• As with an SQL query, the FROM clause names the source of the data for the MDX query. However, unlike an SQL query, the FROM clause in an MDX query is restricted to a single cube. Information from other cubes can be retrieved, however, on a value-by-value basis using the LookupCube function.
  
  
• The WHERE clause is used to describe the slicer dimensions. If a dimension is not mentioned as part of the WHERE clause, Microsoft® SQL Server™ 2000 Analysis Services assumes that any dimension not assigned to an axis dimension is a slicer dimension, and the dimension is filtered on its default members. The WHERE clause can change the filtering process for specified dimensions, allowing fine control of included data.