A tabular model defined in DAX can be queried using MDX because Microsoft has added support for the Multidimensional Expressions (MDX) language in Analysis Services Tabular mode starting with SQL Server 2012. This was done to allow existing MDX-based client tools, such as Excel PivotTables, to connect to and query a Tabular model.
There are several use cases for querying a Tabular model using MDX:
1. Compatibility with existing client tools: As mentioned above, some client tools, such as Excel PivotTables, are designed to work with MDX and may not support DAX. By providing support for MDX in Tabular mode, Microsoft allows these tools to work with Tabular models.
2. Cross-compatibility with other data sources: MDX is a widely used language for querying multidimensional data sources, such as OLAP cubes. By providing support for MDX in Tabular mode, Microsoft allows Tabular models to be queried using the same language as other data sources, which can simplify integration and interoperability.
3. Advanced calculations: While DAX is a powerful language for defining calculations in a Tabular model, MDX provides more advanced functionality for complex calculations and analysis. In some cases, it may be more efficient or easier to define a calculation using MDX rather than DAX.
4. Backward compatibility: Some organizations may have existing MDX-based reports or queries that need to be migrated to a Tabular model. By providing support for MDX in Tabular mode, Microsoft makes it possible to migrate these queries without having to rewrite them in DAX.
In summary, while DAX is the primary language for defining calculations in a Tabular model, MDX provides compatibility with existing client tools, cross-compatibility with other data sources, advanced calculations, and backward compatibility with existing queries.
