Summarizing Query Results (Visual Database Tools)
When you create aggregate queries, certain logical principles apply. For example, you cannot display the contents of individual rows in a summary query. The Query and View Designer helps you comply with these principles in the way the Diagram pane and Criteria pane behave.
By understanding the principles of aggregate queries and the Query and View Designer's behavior, you can create logically correct aggregate queries. The overriding principle is that aggregate queries can result only in summary information. Thus, most of the principles that follow describe the ways that you can reference individual data columns within an aggregate query.