Not sure what you mean, but the following will give you the average of all three fields (individually).
Code:
Select [B][COLOR=#ff0000]SomethingtoGroupon[/COLOR][/B], Avg(Field1), Avg(Field2), Avg(Field3)
From MyTable
Group By [COLOR=red][B]SomethingtoGroupon[/B][/COLOR]
Note that SomethingtoGroupon must be at least one additional field, and that all non-grouped Fields must appear in the Group By Statement.