Sql Server 2008 Reporting Services: Using two dataset error

Question

Im building a report that's using two datasets. when I preview I find these types of errors...

Error 19
[rsFieldReferenceAmbiguous]
The Value expression for the text box ‘Textbox3’ refers directly to the field ‘PerZipCode’ without specifying a dataset aggregate. When the report contains multiple datasets, field references outside of a data region must be contained within aggregate functions which specify a dataset scope.

What aggregate function is needed and where is there an option to set this?

Answer 1

If you are adding multiple datasets to a report, the above may not fix your problem. You may just get the following error when you aggregate it:

[rsMissingAggregateScope] The Value expression for the text box ‘textbox6’ uses an aggregate expression without a scope. A scope is required for all aggregates used outside of a data region unless the report contains exactly one dataset.

What you may need is something like :

First(Fields!MyField.Value, "DATASETNAME")

Which you can get by using the Expression Builder, rather than the drag and drop of fields from the dataset.

Answer 2

Min or Max or Avg etc: most of these

The aggregate is needed to reduce the other DataSet to one value (max of values etc) because you are using something not in the local scope (eg the DataSet bound to the Data Region). There is no way to match rows in the other DataSet with the local scope DataSet.

If your text box is standalone (not in a Data region), the same applies: the aggregate is needed to tell SSRS which row to take (Max etc) or what calculation to do on the dataset (Avg etc)