Allow Unique Index on Columns that intersect the distribution column
If SET tables aren't available, at least allow an UNIQUE INDEX to be placed on a table if the DISTRIBUTION column is found in the columns of the UNIQUE INDEX
Table with location_id and product_id with any number of fact columns. Partition the table by product_id. All the data for any product_id will be on one specific distribution. Allow that distribution to enforce uniqueness on location_id + product_id.