【SQL进阶】纯SQL也能实现小算法（辅助决策）计算商品重要度、是否需要及时补货

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select p_type,p_name, (p_view/view_avg)*0.3+(sales/sales_avg)*0.7 as weight 
from (select a.*,b.sales_avg,c. view_avg  
from (select p_type,a.p_name,a.p_view, IFNULL(b.p_sales,0) as sales from products a  
LEFT JOIN products_sales b on a.p_id=b.p_id
GROUP BY  a.p_type,a.p_name order by a.p_type desc, a.p_view desc 
) a ,
( select p_type,round(sum(sales)/count(*),0) as sales_avg 
from ( select  p_type, a.p_name,a.p_view, IFNULL(b.p_sales,0) as sales from products a  
LEFT JOIN products_sales b on a.p_id=b.p_id
GROUP BY  a.p_type,a.p_name order by a.p_type desc, a.p_view desc ) c
where c.sales>0
GROUP BY p_type
) b,
(select p_type,round(sum(p_view)/count(*),0) as view_avg from products GROUP BY p_type ) c
where a.p_type=b.p_type and a.p_type=c.p_type ) aa