I think you might be able to do it more easily by adding columns to your products table like:
DiscountMin1
DiscountAmount1
and
DiscountMin2
DiscouneAmount2
and
DiscountMin3
DiscountAmount3
Then add all 6 of those to the cart columns as well. Then your rules can be written to be based entirely on a cart column and not depend on productIDs at all.
Then add a calculated column for:
QuantityDiscount = (([Quantity]>[DiscountMin1])?[Price]*[DiscountAmount1]:0) + (([Quantity]>[DiscountMin2])?[Price]*[DiscountAmount2]:0) + (([Quantity]>[DiscountMin3])?[Price]*[DiscountAmount3]:0)
Then add a few more calculated columns:
NewPrice = [Price]-[QuantityDiscount]
RowDiscount = [QuantityDiscount] * [Quantity]
Then you could update the TotalPrice calculation to be: [NewPrice] * [Quantity]
and then you wouldn't even need to add a discount rule at all since it would be included in the cart.
Of course you could also keep the TotalPrice calculation as it is and use a discount rule instead. It would just be set as a discount equal to the sum of the RowDiscount column.
