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.DX 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.