@Samyz
In Direct Query mode, certain functions in both Power Query and DAX are not supported due to limitations in how the data is accessed and processed directly from the underlying data source. Here are some reasons why certain functions may not be supported in Direct Query mode:
1. **Performance Considerations**: Some functions may require extensive computation or access to data that cannot be efficiently processed directly by the data source. This can lead to performance issues or increased load on the data source, making it unsuitable for Direct Query mode.
2. **Data Source Limitations**: Direct Query mode relies on the capabilities of the underlying data source. If the data source does not support certain operations or functions, they cannot be used in Direct Query mode.
3. **Data Source Security**: Some functions may pose security risks or require elevated privileges to execute directly on the data source. In Direct Query mode, the data source's security policies and restrictions apply, limiting the use of certain functions.
4. **Data Consistency**: Certain operations, such as table joins or transformations, may not be feasible to perform directly on the data source while maintaining consistency and integrity across the dataset. In such cases, these operations are typically performed in Power BI's internal engine in Import mode.
As for a list of unsupported functions in Direct Query mode, it can vary depending on the specific data source and version of Power BI. Microsoft's official documentation for Direct Query mode typically includes information on supported and unsupported features for each data source type. Additionally, community forums and user groups may provide insights into specific limitations and workarounds for different scenarios.
For UNION operations in Power BI, you can achieve this using the "Append Queries" feature in Power Query. This allows you to combine multiple tables or queries with the same schema into a single table. However, if your requirement involves combining tables with different schemas, you may need to perform this operation outside of Power BI before importing the data.
Overall, when working with Direct Query mode, it's essential to understand the capabilities and limitations of your data source and choose the appropriate approach for data transformation and analysis based on your specific requirements and constraints.
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