When designing a Power BI project in DirectQuery mode, which statement is correct?

In DirectQuery mode, Power BI maintains a live connection to the data source, meaning that queries to the database are made in real time. One of the key limitations of DirectQuery is that certain transformations available in the Power Query Editor are not supported, including changes to data types of columns after the data has been loaded. Therefore, the statement that you cannot convert column data types is accurate. This restriction is designed to preserve the performance benefits of DirectQuery, as it relies heavily on the underlying data source for processing data on the fly.

In contrast, the other statements do not reflect the limitations correctly. For instance, while DAX functions can be used, some may not work as expected in a DirectQuery context, particularly those that require data manipulation that is only available in Import mode. Additionally, the requirement for data to come from multiple sources is not a restriction of DirectQuery; rather, it can use a single source or multiple sources. Measures can be added, but there are specific limitations on how and where they can be calculated in DirectQuery mode, especially in relation to performance and data aggregation. Hence, the most accurate statement concerning the characteristics of DirectQuery is related to the inability to convert column data types.