Database Reference
In-Depth Information
DirectQuery with Tabular Models
DirectQuery is a deployment option available in Tabular Models, which allows the de-
veloper to use the relational data instead of the in-memory data in the model. This
feature is still immature and needs to be understood to determine how this can be
used.
Data sources
DirectQuery can only use SQL Server and SQL Server PDW databases as sources.
No other relational or non-relational sources are supported including Oracle, SQL
Server Analysis Services or files. In this case, using DirectQuery would be valuable
if using a SQL Server data source and either real-time changes or large data volume
are required in your solution.
Security
The role-based security in the Tabular Model is not supported with DirectQuery. The
security within the data source, however, is supported.
Design limitations
Calculated columns are not supported in a table based on a DirectQuery source.
While calculated measures and KPIs are supported, the DAX formula support is lim-
ited. It is possible to use derived columns in the source to overcome some of the cal-
culation issues. Even these workarounds may not have the desired results as there
are also cases where the calculations differ between the standard Tabular Model and
DirectQuery model. This is caused because the SQL Server engine and the xVelocity
engine can handle these calculations slightly differently.
Client restrictions
Only clients who work with DAX are able to interact with a model using DirectQuery.
This eliminates many tools such as SQL Server Reporting Services and Excel Pivot
Tables. They do work with Power View reports.
Search WWH ::
Custom Search