減值

Question

我有三個表：

1. Plans(PlanID(key), Capacity)
2. CustomerInProject(VahedID, cinpid(key))
3. Vahed(VahedID(key), PlanID,...)

此查詢顯示房子有相同數量的PlanID（地圖）那個人僱用的：

select 
    count(*) 
from 
    Vahed as v2, 
    CustomerInProject 
where 
    CustomerInProject.VahedID = v2.VahedID 
group by PlanID 

Plans有一個int字段名爲Capacity。我想從上面的查詢中減去Capacity。我怎樣才能做到這一點？

Answer 1

像這樣的東西應該這樣做：

select p.PlanID, count(*) - p.Capacity 
from Vahed as v2 
join CustomerInProject c 
    on c.VahedID = v2.VahedID 
join Plan p 
    on p.PlanID = c.PlanID /* or v.PlanID, it's not clear from the question */ 
group by p.PlanID, p.Capacity 

六號線，你可能需要更換c.PlanID與v.PlanID - 我不知道確切的表模式。

Answer 2

select sum(cnt) 
    from 
    (select capacity*-1 as cnt from 
    plans 
    union 
    select count(*) as cnt from Vahed as v2 
inner join 
     CustomerInProject on 
     CustomerInProject.VahedID = v2.VahedID 
     group by PlanID)