Q:

I need to join four dataset results into one tablix

I have four datasets that get information for four different things (a unique set of fields for each one), but that can be joined using a field they share.  I need to get them all into a tablix that will have four rows, one for each dataset per the linking field.  How do I do that?
Currently I can only put in values from one dataset.

A:

Often the best idea would be to create a query that joins the datasets in the sql. If that is not possible, you can look into using the Lookup function to find info from other datasets in your report. The related Lookupset function is able to retrieve sets of information and may be useful as well.

