Multidimensional Expressions

Multidimensional Expressions (MDX) is a query language for online analytical processing (OLAP) using a database management system. Much like SQL, it is a query language for relational databases. It is also a calculation language, with syntax similar to spreadsheet formulas.

The MultiDimensional eXpressions (MDX) language provides a specialized syntax for querying and manipulating the multidimensional data stored in OLAP cubes. While it is possible to translate some of these into traditional SQL, it would frequently require the synthesis of clumsy SQL expressions even for very simple MDX expressions. MDX has been embraced by a wide majority of OLAP vendors and has become the standard for OLAP systems.

MDX was first introduced as part of the OLE DB for OLAP specification in 1997 from Microsoft. It was invented by the group of SQL Server engineers including Mosha Pasumansky. The specification was quickly followed by commercial release of Microsoft OLAP Services 7.0 in 1998 and later by Microsoft Analysis Services. The latest version of the OLE DB for OLAP specification was issued by Microsoft in 1999.

While it was not an open standard, but rather a Microsoft-owned specification, it was adopted by a wide range of OLAP vendors.

The XML for Analysis specification referred back to the OLE DB for OLAP specification for details on the MDX Query Language. In Analysis Services 2005, Microsoft added some MDX Query Language extensions like subselects. Products like Microsoft Excel 2007 started to use these new MDX Query Language extensions. Some refer to this newer variant of MDX as MDX 2005.

In 2001 the XMLA Council released the XML for Analysis (XMLA) standard, which included mdXML as a query language. In the XMLA 1.1 specification, mdXML is essentially MDX wrapped in the XML <Statement> tag.

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