Using IIF Statements Inside A Query?

Hi,

I'm wondering if it is possible to use IF statements in a query, for example if this was my query:

SELECT Asset, Source, Val1, Val2, Val3
FROM tableA

Say the sign of the Vals is always positive, but based on if the Source field is null i want to make the Vals negative.
Could I do something like this:

SELECT Asset, Source, (IIF Source = null, Val1*-1, Val1), (IIF Source = null, Val2*-1, Val2), (IIF Source = null, Val3*-1, Val3)
FROM tableA


When I try something like this it doesn't work, is there a way to do this in a query?

Thanks.