MultiDimensional Expressions (MDX)
is a query language for OLAP
databases, much like SQL 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 de facto
standard for OLAP systems. "