One way to do this is to create another field equal to the value you want totaled if the condition is met, but null if not. For example:
Case ( Year ( dateSold ) = Year ( datePurchased ) ; cost ; "" )
would give you the cost of the item if it was sold during the same year it was purchased. Otherwise, it'd be empty. You could then base your sum on this field instead of the cost field.
This method adds overhead to the database, but a SQL SUM likely would too.
You could define a calc CompleteValue as: If (Status = "complete"; value; 0) and sum on it.
Along the same lines, you could just add another number field, and populate it with a triggered script. Not sure it would make a whole lot of difference in the overhead, but it is another method.
THANKS to all,
I just created another field on the child table with an IF & summed up it.
Keeps it easy, thanks again.