select category product_category
, age_group
, sum(quantity*price) total_sales_amount
, round(sum(quantity*price)/sum(sum(quantity*price)) over(partition by category),2)purchase_percentage
from sales s
left join products p on s.product_id = p.product_id
left join customer_info c on s.sale_id = c.sale_id
group by 1,2
order by 1,2