Print the product code, name, and discount percentage of each product that has the same discount percentage as another product. Do not print a product more than once. Sort the query result in the increasing order of product code. HINT: need to use a self join.

For each category that has at least one product, print its id, name, and the id and name of each product in that category. Sort the result in the increasing order of category id. HINT: need to use an inner join.

For each product category, print its id, name, and the id and name of each product in that category. Include categories without any product in the query result. Sort the result in the increasing order of category id. HINT: need to use an outer join.