最佳查询收视率数据库？

Question

我有一张存储用户ID，对象ID和分数（+1或-1）的评分表。现在，当我想显示一个对象列表，其总分数，+1票数和-1票数。

我怎样才能有效地做到这一点，而不必做SELECT COUNT（*）FROM评分WHERE（score = +/- 1 AND object_id = ..）？这是每个对象显示的两个查询，这是不可接受的。数据库设计是否合理？

Answer 1

虽然它并没有解决您的合理设计问题，这里，让你一次这两个方面的查询：

select 
    sum(case when score = 1 then 1 else 0 end) 'positive' 
, sum(case when score = -1 then 1 else 0 end) 'negative' 
, objectId 
from 
    ratings 
where 
    objectId = @objectId ... 
group by 
    objectId 

Answer 2

select object_id, 
     sum(case when score = 1 then 1 else 0) upvotes, 
     sum(case when score = -1 then -1 else 0) downvotes, 
     sum(score) 
from ratings 
group by object_id 

也许类似的东西。

Answer 3

这应做到：

SELECT 
    UserID, ObjectID, 
    SUM(CASE WHEN score=1 Then 1 Else 0 End) as UpVotes, 
    SUM(CASE WHEN score=-1 Then 1 Else 0 End) as DownVotes, 
FROM YourTable 
GROUP BY UserID, ObjectID