Can you provide the second highest and second lowest sales items? Also, can you give the most viable product, defined as having the lowest return rate and highest sales?

SELECT product_name
FROM (
  SELECT product_name,
         SUM(Sale_Quantity) AS total_sales,
         RANK() OVER (ORDER BY SUM(Sale_Quantity) DESC) AS rank_desc,
         RANK() OVER (ORDER BY SUM(Sale_Quantity) ASC) AS rank_asc
  FROM sales_table
  GROUP BY product_name
) AS ranked
WHERE rank_desc = 2 OR rank_asc = 2;

SELECT product_name
FROM (
  SELECT product_name,
         SUM(Sale_Quantity) AS total_sales,
         SUM(Return) AS total_return,
         SUM(Return) / NULLIF(SUM(Sale_Quantity),0) AS return_rate
  FROM sales_table
  GROUP BY product_name
) AS metrics
ORDER BY return_rate ASC, total_sales DESC
LIMIT 1;