I'm trying to build a view where I can vary the fields I'm grouping on, based on passed parameters.

SELECT State, OrderDate, ItemCode, count(*) FROM mytable ;
WHERE IIF(EMPTY(?vp_state), "Ignore State", "Group by State") ;
  AND IIF(EMPTY(?vp_orderdate), "Ignore OrderDate", "Group by OrderDate") ;
  AND IIF(EMPTY(?vp_itemcode), "ItemCode", "Group by ItemCode") ;
GROUP BY 1,2,3

*Pass State:
State  OrderDate  ItemCode  Count
TX     {}         ''        5
NM     {}         ''        3

*Pass OrderDate:
State  OrderDate  ItemCode  Count
''     {7/1/2006} ''        2
''     {8/1/2006} ''        6

*Pass State and OrderDate:
State  OrderDate  ItemCode  Count
TX     {7/1/2006} ''        1
TX     {8/1/2006} ''        4
NM     {7/1/2006} ''        1
NM     {8/1/2006} ''        2

Is there a good way to pull this off without multiple views or SQL Passthrough? I've looked at macro substituting WHERE and GROUP BY clauses, but not getting the results I want.