you can also use a function like this
Public Function maxDate(ParamArray dtmDates() As Variant) As Variant
Dim dtmDate As Variant
For Each dtmDate In dtmDates
If (IsDate(dtmDate) Or IsNull(dtmDate)) And dtmDate > maxDate Then maxDate = dtmDate
Next dtmDate
End Function
then in a query
SELECT tblDates.ID, tblDates.field1, tblDates.field2, tblDates.field3, maxDate([field1],[field2],[field3]) AS maxDate
FROM tblDates;
And as Skip pointed out this assumes that the max date is what you are asking.