> For the complete documentation index, see [llms.txt](https://docs.pentaho.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.pentaho.com/install/10.2-install/multidimensional-data-modeling-in-pentaho/about-multidimensional-expression-language.md). # Multidimensional Expression Language The Multidimensional Expression Language (MDX) is an OLAP database query and calculation language similar to SQL. It is the method by which a dataset is retrieved from a OLAP database. While you do not necessarily have to know MDX in order to use Pentaho's client tools, you should be somewhat familiar with it for the purpose testing your Mondrian schema. ### MDX Syntax If you are already familiar with SQL, then much of the MDX syntax will look familiar, and the rest should be relatively easy to learn. You can edit the MDX using Analyzer or a text editor. There are six MDX data types: * Dimension or hierarchy * Level * Member * Tuple * Scalar * Set Below is an example of a very simple MDX query: ``` SELECT { [Measures].[Salesfact] } ON COLUMNS, { [Date].[2004], [Date].[2005] } ON ROWS FROM Sales ``` MDX was initially developed by Microsoft for its SQL Server analysis products, though it has since become an independent standard. It's been around long enough now that there are many MDX tutorials and references, most notably: * * MDX implementations vary, and many MDX documentation resources are specific to certain niche products or standards. Not all MDX functions and extensions are supported in Pentaho Analysis. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.pentaho.com/install/10.2-install/multidimensional-data-modeling-in-pentaho/about-multidimensional-expression-language.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.