>Ok, but does that mean that I include all the fields I mentioned? What about the IIF that uses two fields? Or do I use numbers for every column I'm going to create that is not a SUM?
>

select iif(field1=3,field2,field1) as expr1, field2, sum(field3) as sum from myTable group by 1,2

For all non aggregate column you should put them into Group by. You can not use Memo field in your select.