It sounds like a discount rule, each rule triggers a different type of discount in code, the discount is probably a class module, with new discounts being applied in the class moduel. soemtimes you can do the discount entirely in SQL depending oin complex the discount rule is, and how transparent your data is.
it depends on how tightly the rule is drawn up
you would need some mechanism to identify what are qualifying products, and what products qualify for one category but not another category.
so it maybe that the manufacturer has to be the same, the manufacturer product has to be the same. most manufacturers treat a shirt of design x the same but qualify their stock number with some trailing digits to indicate size or colourway
it may also depend on how many special offers the customer has running concurrently, and how often they change them
I'd suspect the customer needs to qualify their product range with some coding so that you can base a discount rule. That coding may well involve using the manufacturer stock number.
you need cleear guidance from the customer as to how they structure their offers
its could be
buy x products from manufacturer y get n% discount
buy x products from the same product range from this manufacturer
buy x shorts, irrespective of manufacturer or size
or much tighter buy x shirts of the same design but different colours, or sizes
until you have got that bottomed out Im not sure you can progress further
the discount rule could be the detail SQL, or a reference to the stored query identifying the the SQL to apply the discount.. mebbe move the business logic applying the discount to a specific stored procedure.. specific to each discount offer