General Characteristics of Data Retrieved From a Report Data Source
To retrieve Reporting Services report data from a data source, the data provider corresponding to the data source type passes the query command text for each report dataset or report parameter and retrieves the results.
Data retrieved from a report data source is expected to follow these general conventions:
The data retrieved is a single rowset. If multiple rowsets are retrieved through a single query, only the first rowset is processed.
For multidimensional and XML data sources, data is retrieved as a flattened rowset.
In addition, when you define a report dataset, you can set data properties directly or accept the defaults set by the data provider. Properties include case, kanatype, width, accent and collation. For more information about how to set these properties, see Dataset (Data Options Tab, Report Designer).
Retrieving scalar values directly is not supported. Scalar values can be retrieved by wrapping the value in a SELECT statement and returning the value as a rowset that has a single column and a single row. To access the scalar value from its report dataset, use an expression with the FIRST function with scope variable set to its dataset. For example,