题解 | 每个商品的销售总额

思路：先聚合、再排序

错误点：group by 后的字段必须在select里

with tmp as (
    select o.product_id
           , p.category
           , p.name as product_name
           , sum(o.quantity) as total_sales
    from products p
    join orders o
    on p.product_id = o.product_id
    group by o.product_id, p.name, p.category
)

select product_name
       , total_sales
       , row_number() over(partition by category order by total_sales desc, product_id) as category_rank
from tmp