CountDistinct Function (Reporting Services)
Returns a count of all distinct values of the specified expression.
(Variant) The expression on which to perform the aggregation. The expression cannot contain aggregate functions.
(String) The name of a dataset, grouping, or data region that contains the report items to which to apply the aggregate function. If Scope is specified, the aggregate function applies to all data in the dataset, grouping, or data region. For more information about the Scope parameter, see Using Report Functions in Expressions (Reporting Services).
The following code example provides a count of managers in the Department grouping or data region.