Ultimately I would probably set things up differently. But to stick with your current setup, what you can do is create a template column that joins Business and Category together. Using that template, create a single relation back to itself. Then create a Lookup column that returns the Row ID from the relation. Finally create an IF column that checks if the Row ID matches the Lookup Row ID. If it’s a match, then return true, else false. Or you could probably just have the IF column return the Category name. This will give you a boolean value of true (or Category name) only in the rows that have that Business/Category combination the first time it appears in the data.