Get top 10 products for every category

Question

I have a query which is something like this

SELECT 
t.category, 
tc.product, 
tc.sub-product,
 count(*) as sales 
 FROM tg t, ttc tc
 WHERE t.value = tc.valu         


        

Answer 1

It's guesswork, but you could probably start from something like this:

drop table category_sales;

Some test data:

create table category_sales (
   category    varchar2(14),
   product     varchar2(14),
   subproduct  varchar2(14),
   sales       number
);

begin

  for cate in 1 .. 10 loop
  for prod in 1 .. 20 loop
  for subp in 1 .. 30 loop

      insert into category_sales values (
             'Cat '  || cate,
             'Prod ' || cate||prod,
             'Subp ' || cate||prod||subp,
              trunc(dbms_random.value(1,30 + cate - prod + subp))
      );

  end loop; end loop; end loop;

end;
/

The actual query:

select * from (
  select 
    category,
    product,
    subproduct,
    sales,
    category_sales,
    product_sales,
    top_subproduct,
    -- Finding best products within category:
    dense_rank () over (
      partition by category
      order     by product_sales desc
    ) top_product 
  from (
    select 
      -- Finding the best Subproducts within
      -- category and product:
      dense_rank () over (
         partition by category, 
                      product 
         order     by sales desc
      )                             top_subproduct,
      -- Finding the sum(sales) within a 
      -- category and prodcut
      sum(sales) over (
         partition by category, 
                      product
      )                             product_sales,
      -- Finding the sum(sales) within 
      -- category
      sum(sales) over (
         partition by category
      )                             category_sales,
      category,
      product,
      subproduct,
      sales
    from
      category_sales
  )
)
where 
--    Only best 10 Products
      top_product       <= 10 and
--    Only best 5 subproducts:
      top_subproduct    <= 5
-- "Best" categories first:
order by 
      category_sales desc,
      top_product    desc,
      top_subproduct desc;

In that query, the column category_sales returns the sum of sales of the category in whose record it is returned. That means, every record of the same category has the same category_sales. This column is needed to order the result set with the best (sales) categories first (order by ... category_sales desc).

Similarly, product_sales is the sum of sales for a category-product combination. This column is used to find the best n (here:10) products in each category (where top_product <= 10).

The column top_product is "created" with the dense_rank() over... analytical function. For the best product in a category,it's 1, for the second best it's 2 and so on (hence the where top_product <= 10.

The columntop_suproduct is calculated in a similar fashion like top_product (that is with dense_rank).