表一：

表二：

-- 问题，表一是总库存表，表二是销售记录表求剩余库存
SELECT
    tsi.type,
    (tsi.last_count - if(t.sales,
    t.sales,
    0) 
    )  as remaining_invetory 
from
    t_shop_info tsi
left join (
    SELECT
        type as type_a ,
        sum(sale_count) as sales
    from
        t_sale_info
    group by
        type 
        ) t on
    tsi.`type` =