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According to the documentation...
PARENT/CHILD RELATION REFERENCING
A column in a child table may be referenced in an expresion by prepending the column name with "Child." For example, "Child.Price" would reference the column named Price in the child table.
If a table has more than one child, the syntax is: Child(RelationName). For example, if a table has two child tables named Employee and Titles, and the DataRelation objects are named "Publishers2Employee: and "Publishers2Titles," the reference would be:
Child(Publishers2Employee).fname
Child(Publishers2Titles).title
A parent table may be referenced in an expression by prepending the column name with "Parent." For example, the "Parent.Price" references the parent table's column named "Price."
AGGREGATES
The following aggregate types are supported:
Sum (Sum)
Avg (Average)
Min (Minimum)
Max (Maximum)
Count (Count)
StDev (Statistical standard deviation)
Var (Statistical variance).
Aggregates are usually performed along relationships. Create an aggregate expression by using one of the functions listed above and a child table column as detailed in PARENT/CHILD RELATION REFERENCING above. For example:
Avg(Child.Price)
Avg(Child(Orders2Details).Price)
An aggregate can also be performed on a single table. For example, to create a summary of figures in a column named "Price":
Sum(Price)
Note If you use a single table to create an aggregate, there would be no group-by functionality. Instead, all rows would display the same value in the column.
If a table has no rows, the aggregate functions will return a null reference (Nothing in Visual Basic).
Data types can always be determined by examining the DataType property of a column. You can also convert data types using the Convert function, shown below.