Select Fields on the Dataset Properties dialog box to change the field collection for the report dataset. The fields list is automatically populated, but you can use Fields to add, edit, and delete query and calculated fields.
Add a new query or calculated field to the dataset.
Delete the selected field from the dataset.
Type a name for the field. The field must be unique within the dataset. For each existing field in the dataset, the name is pre-populated.
Enter a value for the field.
For a calculated field, the field source must be the name of an existing field retrieved by the dataset query, or an expression that you create. For example, to create a field that represents 10 times the value in the query field Sales, use the expression =10 * Fields!Sales.Value.
For a query field, the field source must be the name of an existing field retrieved by the dataset query.
Add or change an expression for the new calculated field. This button only appears when you click Add and select Calculated Field.