Multidimensional expressions

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Multidimensional Expressions ( MDX ) is a query language for OLAP - database . It was developed by Microsoft and is establishing itself as the industry standard . Overall, MDX is very complex and powerful. The academic side has criticized MDX for the fact that there is no complete definition of the language and that it only appears to be based on SQL . MDX is used as the standardized query language of OLE DB for OLAP (ODBO) and XML for Analysis .

Components

The basic components of MDX are measures and dimensions , which correspond to the facts and dimensions of a data warehouse . The dimensions consist of a set of members (classification nodes) that are connected to each other in different levels (classification levels ) via multiple hierarchies (classification paths), which can be used for aggregation . The members must each be clearly identified.

Requests

An MDX request generally has the following form: 

SELECT axis ON COLUMNS, axis ON ROWS, ...
FROM cube

WHERE slice

In this case, be of a generally OLAP cube (English cube ; FROM) a set of dimensions and belonging to them, classification nodes selected ( SELECT) and on different axes of the result table ( COLUMNS, ROWS, PAGESready ...). With a slice ( WHERE) a selection can be made within the facts.

Character strings are identified as names with simple square brackets. Curly brackets are used to define sets.

Example of an MDX request 

SELECT {[Measures].[Unit Sales],[Measures].[Store Cost]} ON COLUMNS,
 order(except([Promotion Media].[Media Type].members,
              {[Promotion Media].[Media Type].[No Media]}),
       [Measures].[Unit Sales],DESC) ON ROWS
FROM Sales

literature

Web links