Q:

Is it possible for me to include a sub report in a tablix row that is grouped by an ID?

Is it possible for me to include a sub report in a tablix row that is grouped by an ID and pass that ID into the sub-report to be ran?  Basically, the sub-report would return data from a second dataset based off of the ID that is being used in the grouping of the main tablix?
My main tablix has 4 rows that are grouped together by an ID where i create a few graphs from a main dataset.  My second dataset returns simulations that can contain hundreds of rows per ID, which is why I don't want to do this in a join statement because it is extremely ineffecient.  I want to add a tablix to row 5 within my main tablix and display the results from dataset2, but only have it run within the current group of Tablix1.
Dataset1 would be similar to this with a unique iGoalID for each group in the main tablix.

Dataset2 would look like this;

I'd like to be able to loop through DataSet2 and display the data, but only grouped by the main tablix iGoalID equaling dataset2's iGoalID

A:

You have to build the subreport as a separate report .rdl and build it to accept a parameter of the ID.  You will then pass the ID parameter to the subreport once it's added to the parent report.  Once the sub is built, tested, and saved...add it to your main report using Insert-> Subreport on the main tab.  You should be able to select the cell on the design view where you want the subreport to be and insert the subreport there.
To specify parameters to pass to a subreport

In Design view, right-click the subreport and then click Subreport
Properties. 

In the Subreport Properties dialog box, click
Parameters. Click Add. A new row is added to the parameter grid. 
In the Name text box, type the name of a parameter in the subreport or
choose it from the list box. This name must match a report
parameter, not a query parameter, in the subreport. 
In the Value list box, type or select a value to pass to the subreport. This
value can be static text or an expression that references a field or
other object in the main report.

